Analysis and Interpretation of Igneous Rocks IGNEOUS ROCKS WORKSHEET Sample Number or Letter Texture(s) Present (Figure 5.4) Minerals Present and Their % Abundance (Figure 5.4) Mafic Color Index (Figure 5.5) Rock Name from Figure 5.4 or 5.5 How Did the Rock Form Relative to Bowen’s Reaction Series (Figure 5.6) and Intrusive/Extrusive Processes? Name: ______________________________________ Course/Section: ______________________ Date: ___________ 150 ACTIVITY Sample Number or Letter Texture(s) Present (Figure 5.4) Minerals Present and Their % Abundance (Figure 5.4) Mafic Color Index (Figure 5.5) Rock Name from Figure 5.4 or 5.5 How Did the Rock Form Relative to Bowen’s Reaction Series (Figure 5.6) and Intrusive/Extrusive Processes? 151 Name: ______________________________________ Course/Section: ______________________ Date: ___________ IGNEOUS ROCKS WORKSHEET 7.3 Hand Sample Analysis, Classification, and Origin METAMORPHIC ROCKS WORKSHEET Sample Letter or Number Texture(s) (Figure 7.16—Step 1) foliated nonfoliated foliated nonfoliated foliated nonfoliated foliated nonfoliated foliated nonfoliated Mineral Composition and Other Distinctive Properties (Figure 7.16, Step 2) Rock Name (Figure 7.16, Step 3) Parent Rock (Figure 7.16, Step 4) Uses (Figure 7.16, Step 5) Name: ______________________________________ Course/Section: ______________________ Date: ____________ ACTIVITY ACTIVITY MINERAL DATA CHART Luster* Hardness Cleavage Color Streak 105 *M = metallic or submetallic, NM = nonmetallic Fracture Other notable properties; tenacity, magnetic attraction, reaction with acid, specific gravity, smell, etc Name (Fig. 3.18, 3.19, or 3.20) and chemical composition (Fig. 3.21) How do you depend on this mineral or elements from it? (Fig. 3.21) Name: ______________________________________ Course/Section: ______________________ Date: ____________ Sample Letter or Number 3.4 Mineral Analysis, Identification, and Uses MINERAL DATA CHART Luster* Hardness Cleavage Color Streak *M = metallic or submetallic, NM = nonmetallic Fracture Other notable properties; tenacity, magnetic attraction, reaction with acid, specific gravity, smell, etc Name (Fig. 3.18, 3.19, or 3.20) and chemical composition (Fig. 3.21) How do you depend on this mineral or elements from it? (Fig. 3.21) Name: ______________________________________ Course/Section: ______________________ Date: ____________ 106 Sample Letter or Number MINERAL DATA CHART Luster* Hardness Cleavage Color Streak 107 *M = metallic or submetallic, NM = nonmetallic Fracture Other notable properties; tenacity, magnetic attraction, reaction with acid, specific gravity, smell, etc Name (Fig. 3.18, 3.19, or 3.20) and chemical composition (Fig. 3.21) How do you depend on this mineral or elements from it? (Fig. 3.21) Name: ______________________________________ Course/Section: ______________________ Date: ____________ Sample Letter or Number MINERAL DATA CHART Luster* Hardness Cleavage Color Streak *M = metallic or submetallic, NM = nonmetallic Fracture Other notable properties; tenacity, magnetic attraction, reaction with acid, specific gravity, smell, etc Name (Fig. 3.18, 3.19, or 3.20) and chemical composition (Fig. 3.21) How do you depend on this mineral or elements from it? (Fig. 3.21) Name: ______________________________________ Course/Section: ______________________ Date: ____________ 108 Sample Letter or Number Sample Number or Letter Composition (Figures 6.2 and 6.9) Textural and Other Distinctive Properties (Figures 6.3 and 6.9) Rock Name (Figure 6.9) How Did the Rock Form? (See Figure 6.10) Name: ______________________________________ Course/Section: ______________________ Date: ____________ 180 SEDIMENTARY ROCKS WORKSHEET BIG IDEAS PRE-LAB VIDEO Minerals comprise rocks and are described and classified on the basis of their physical and chemical properties. Every person depends on minerals and elements refined from them, but the supply of minerals is nonrenewable, and the magnitude of their use may be unsustainable. FOCUS YOUR INQUIRY | THINK What are minerals and crystals, and how are they About It related to rocks and elements? ACTIVITY 3.1 Mineral and Rock Inquiry (p. 74) THINK About It | How and why do people study minerals? ACTIVITY 3.2 Mineral Properties (p. 77) ACTIVITY 3.3 Determining Specific Gravity (SG) (p. 86) THINK How and why do people study minerals? How do About It you personally depend on minerals and elements extracted from them? L A B O R ATO R Y 3 Mineral Properties, Identification, and Uses ACTIVITY 3.4 Mineral Identification and Uses (p. 88) THINK How do you personally depend on minerals and About It elements extracted from them? How sustainable is your personal dependency on minerals and elements extracted from them? ACTIVITY 3.5 The Mineral Dependency Crisis (p. 89 ) THINK How sustainable is your personal dependency About It on minerals and elements extracted from them? ACTIVITY 3.6 Urban Ore (p. 99) CONTRIBUTING AUTHORS Jane L. Boger • SUNY, College at Geneseo Philip D. Boger • SUNY, College at Geneseo Roseann J. Carlson • Tidewater Community College Charles I. Frye • Northwest Missouri State University Michael F. Hochella, Jr. • Virginia Polytechnic Institute Bingham Canyon Mine, southwest of Salt Lake City, Utah. It is primarily a copper mine, but gold, silver, and other metals have also been extracted from the ore here for over a century. (Michael Collier) 73 ACTIVITY 3.1 Mineral and Rock Inquiry THINK What are minerals and crystals, and how About It are they related to rocks and elements? OBJECTIVE Analyze rock samples, and infer how minerals are related to and distinguished from rocks, crystals, and chemical elements. PROCEDURES 1. Before you begin, do not look up definitions and information. Use your current knowledge, and complete the worksheet with your current level of ability. Also, this is what you will need to do the activity: ____ Activity 3.1 Worksheet (p. 101) and pencil 2. Then answer every question on the worksheet in a way that makes sense to you and be prepared to compare your ideas with others. 3. After you complete the worksheet, read about minerals and rocks below and be prepared to discuss your observations, interpretations, and inferences with others. true minerals normally form by inorganic processes, some organisms make them as shells or other parts of their bodies. These so-called biominerals are of obvious organic origin (made by plants and animals). Examples include aragonite mineral crystals in clam shells and tiny magnetite crystals in the human brain. People make cultured mineral crystals in laboratories. Their chemical and physical properties are identical to naturally-formed mineral crystals, but they are not true minerals because they are synthetic (man-made, not natural). How Are Minerals Classified? Geologists have identified and named thousands of different kinds of minerals, but they are often classified into smaller groups according to their importance, use, or chemistry. For example, a group of only about twenty are known as rock-forming minerals, because they are the minerals that make up most of Earth’s crust. Another group is called the industrial minerals, because they are the main non-fuel raw materials used to sustain industrialized societies like ours. Some industrial minerals are used in their raw form, such as quartz (quartz sand), muscovite (used in computer chips), and gemstones. Most are refined to obtain specific elements such as iron, copper, and sulfur. All minerals are also classified into the following chemical classes: ■ Minerals and Rocks Many people think of minerals as the beautiful natural crystals mined from the rocky body of Earth and displayed in museums or mounted in jewelry. But table salt, graphite in pencil leads, and gold nuggets are also minerals. What Are Minerals? According to geologists, minerals are inorganic, naturally occurring solids that have a definite chemical composition, distinctive physical properties, and crystalline structure. In other words, each mineral ■ ■ ■ ■ occurs in the solid, rocky body of Earth, where it formed by processes that are inorganic (not involving life). has a definite chemical composition of one or more chemical elements that can be represented as a chemical formula (like NaCl for halite, FeS2 for pyrite, and Au for pure “native gold”). has physical properties (like hardness, how it breaks, and color) that can be used to identify it. has crystalline structure—an internal patterned arrangement or geometric framework of atoms that can be revealed by external crystal faces (FIGURES 3.1A, B), the way a mineral breaks (FIGURE 3.2B), and in atomicresolution images (FIGURE 3.2C). A few “minerals,” such as limonite (rust) and opal (FIGURE 3.3) never form crystals, so they do not have crystalline structure. They are mineral-like materials (mineraloids) rather than true minerals. And even though all 74 ■ L A B O R AT O R Y 3 ■ ■ ■ ■ ■ Silicate minerals are composed of pure silicon dioxide (SiO2, called quartz) or silicon-oxygen ions (SiO4)4combined with other elements. Examples are olivine: (Fe, Mg)2SiO4, potassium feldspar: KAlSi3O8, and kaolinite: Al2(Si4O10)(OH)8. Oxide minerals contain oxygen (O2-) combined with a metal (except for those containing silicon, which are silicate minerals). Examples are hematite: Fe2O3, magnetite: Fe2O3, and corundum: Al2O3. Hydroxide minerals contain hydroxyl ions (OH)combined with other elements (except for those containing silicon, which are silicate minerals). Examples are goethite: FeO(OH) and limonite: FeO(OH) # nH2O. Sulfide minerals contain sulfur ions (S2-) combined with metal(s) and no oxygen. Examples are pyrite: FeS2, galena: PbS, and sphalerite: ZnS. When they are scratched or crushed, one can usually smell the sulfur in these minerals. Sulfate minerals contain sulfate ions (SO4)2- combined with other elements. Examples include gypsum: CaSO4 # H2O and barite: BaSO4. Carbonate minerals contain carbonate ions (CO3)2- combined with other elements. Examples include calcite: CaCO3 and dolomite: CaMg(CO3)2. These minerals react with acid, the way baking soda (which is the mineral named nahcolite and the chemical compound named sodium bicarbonate: NaHCO3) reacts with acetic acid (CH3COOH) in vinegar. Geologists use dilute hydrochloric acid (HCl) to detect carbonate minerals because the reaction makes larger bubbles. If a mineral reacts with the dilute HCl, then it is a carbonate mineral. Crystal faces 6 1 2 5 4 3 Crystal faces A. A rock made of two large, visible, quartz mineral crystals. Crystal faces (flat outside surfaces) merge into three dimensional crystal forms (geometric shapes). Crystal growth was unobstructed, except where the two crystals touched and grew together (x1). Top view: Crystal growth was unobstructed so crystal faces are developed (x1). x2 Side view: Deformed crystal faces among crowded intergrown crystals (x1). B. Rock made of many quartz mineral crystals. Note how crystal growth was obstructed as the sides of many crystals grew together (side view), but tips of the crystals (top view) grew unobstructed into six-sided pyramids. Iron impurity gives the purple amethyst variety of quartz its color. C. Crystal growth of the calcite mineral crystals in this rock (marble) was obstructed in every direction. The crystals grew together as a dense mass of odd-shaped crystals instead of perfect crystal forms. Intergrown crystals outlined in black Thin section (x30). The layers of agate are made of long intergrown quartz mineral crystals. D. Slice of rock (agate) cut with a diamond saw and polished. The layers are made of quartz mineral crystals that are cryptocrystalline (not visible in hand sample). They can only be seen in a thin section (thin transparent slice of the rock mounted on a glass slide) magnified with a microscope to 30 times larger than their actual size (x30). FIGURE 3.1 Minerals and rocks. Most rocks are made of one or more mineral crystals. Mineral Properties, Identification, and Uses ■ 75 C. Scanning tunneling microscope (STM) image of galena showing the orderly arrangement of its lead and sulfur atoms. Each sulfur atom is bonded to four lead atoms in the image, plus a lead atom beneath it. Similarly, each lead atom is bonded to four sulfur atoms in the image, plus a sulfur atom beneath it. B. When struck with a hammer, galena breaks along flat cleavage surfaces (planes of weak chemical bonding within the crystal) that have a silvery color, like metal, and intersect at 90° angles to form shapes made of cubes. x1 A. Galena mineral crystals form cubic shapes that tarnish to a dull gray color. ■ ■ ■ Blue = S (sulfur) atoms, Orange = Pb (lead) atoms nm = nanometer = 1 millionth of a millimeter FIGURE 3.2 Crystal shape, cleavage, and atomic structure. Galena is lead sulfide—PbS. It is an ore mineral from which lead (Pb) and sulfur (S) are extracted. (STM image by C.M. Eggleston, University of Wyoming) Halide minerals contain a halogen ion (F-, Cl-, Br-, or I-) combined with a metal. Examples are halite: NaCl and fluorite: CaF2. Phosphate minerals contain phosphate ions (PO4)3combined with other elements. An example is apatite: Ca5F(PO4)3(OH, F, Cl). Native elements are elements in pure form, not combined with different elements. Examples include graphite: C, copper: Cu, sulfur: S2, gold: Au, and silver: Ag. Opal is a residue of hydrated silicon dioxide that forms light-colored translucent masses like this. Notice its lack of crystals and cleavage. This “precious” opal has been polished to enhance its internal flashes of color. How Are Minerals Related to Rocks? Most rocks are aggregates of one or more mineral crystals. For example, mineral crystals comprise all of the rocks in FIGURE 3.1. Notice that you can easily detect the mineral crystals in FIGURES 3.1A and 3.1B by their flat faces, which are an external feature of the internal geometric framework of their atoms. However, the crystals in many rocks have grown together in such a crowded way that few faces are visible (FIGURES 3.1C). Some rocks are also cryptocrystalline, made of crystals that are only visible under a microscope (FIGURE 3.1D). Earth is sometimes called the “third rock” (rocky planet) from the Sun, because it is mostly made of rocks. But rocks are generally made of one or more minerals, which are the natural materials from which every inorganic item in our industrialized society has been manufactured. Therefore, minerals are the physical foundation of both our rocky planet and our human societies. 76 ■ L A B O R AT O R Y 3 Limonite forms dull powdery yellow-brown to dense dark brown masses like this. Notice its lack of crystals and cleavage. It is a residue of hydrated iron oxide and/or hydrated iron oxyhydroxide that you know as rust. FIGURE 3.3 Mineraloids. Opal and limonite are naturallyoccurring inorganic materials, but they are amorphous (noncrystalline; they never form crystals). This makes them mineraloids (amorphous mineral-like materials), rather true minerals, but they are described, identified, and listed as minerals. ACTIVITY 3.2 Mineral Properties THINK About It | How and why do people study minerals? OBJECTIVE Analyze and describe the physical and chemical properties of minerals. PROCEDURES 1. Before you begin, read the following background information. This is what you will need: ____ Activity 3.2 Worksheets (pp. 102–103) and pencil ____ set of mineral samples (obtained as directed by your instructor) ____ set of mineral analysis tools (obtained as directed by your instructor) ____ cleavage goniometer cut from GeoTools Sheet 1 at the back of the manual 2. Then follow your instructor’s directions for completing the worksheets. What Are a Mineral’s Chemical and Physical Properties? The chemical properties of a mineral are its characteristics that can only be observed and measured when or after it undergoes a chemical change due to reaction with another material. This includes things like if or how it tarnishes (reacts with air or water) and whether or not it reacts with acid. For example, calcite and other carbonate (CO3containing) minerals react with acid, and native copper tarnishes to a dull brown or green color when it reacts with air or water. The physical properties of a mineral are its characteristics that can be observed (and sometimes measured) without changing its composition. This includes things like how it looks (color, luster, clarity) before it tarnishes or weathers by reacting with air or water, how well it resists scratching (hardness), how it breaks or deforms under stress (cleavage, fracture, tenacity), and the shapes of its crystals. For example, quartz crystals are hard to scratch, glassy, and transparent, while talc is easily scratched, opaque, and feels greasy. In this activity, you will use the properties of color and clarity (before and after tarnishing), crystal form, luster (before and after tarnishing), streak, hardness, cleavage, and fracture to describe mineral samples. Additional properties— such as tenacity, reaction with acid, magnetic attraction, specific gravity, striations, and exsolution lamellae—can also be helpful in analyzing particular minerals. Color and Clarity. A mineral’s color is usually its most noticeable property and may be a clue to its identity. Minerals normally have a typical color, like gold. A rock made up of one color of mineral crystals is usually made up of one kind of mineral, and a rock made of more than one color of mineral crystals is usually made up of more than one kind of mineral. However, there are exceptions, like the agate in FIGURE 3.1D. It has many colors, but they are simply varieties (var.)—different colors—of the mineral quartz. This means that a mineral cannot be identified solely on the basis of its color. The mineral’s other properties must also be observed, recorded, and used collectively to identify it. Most minerals also tend to exhibit one color on freshly broken surfaces and a different color on tarnished or weathered surfaces. Be sure to note this difference, if present, to aid your identification. Mineral crystals may vary in their clarity: degree of transparency or their ability to transmit light. They may be transparent (clear and see-through, like window glass), translucent (foggy, like looking through a steamedup shower door), or opaque (impervious to light, like concrete and metals). It is good practice to record not only a mineral’s color, but also its clarity. For example, the crystals in FIGURE 3.1B are purple in color and have transparent to translucent clarity. Galena mineral crystals (FIGURE 3.2) are opaque. Crystal Forms and Mineral Habits. The geometric shape of a crystal is its crystal form. Each form is bounded by flat crystal faces that intersect at specific angles and in symmetrical relationships (FIGURE 3.1A and B). The crystal faces are the outward reflection of the way that atoms or groups of atoms bonded together in a three-dimensional pattern as the crystal grew under specific environmental conditions. There are many named crystal forms (FIGURE 3.4). Combinations of two or more crystals can also form named patterns, shapes, or twins (botryoidal, dendritic, radial, fibrous: FIGURE 3.4). A mass of mineral crystals lacking a distinctive pattern of crystal growth is called massive. Development of Crystal Faces. The terms euhedral, subhedral, and anhedral describe the extent to which a crystal’s faces and form are developed. Euhedral crystals have well developed crystal faces and clearly defined and recognizable crystal forms (FIGURE 3.1A). They develop only if a mineral crystal is unrestricted as it grows. This is rare. It is more common for mineral crystals to crowd together as they grow, resulting in a massive network of intergrown crystals with deformed crystal faces and odd shapes or imperfect crystal forms (FIGURE 3.1B). Subhedral crystals are imperfect but have enough crystal faces that their forms are recognizable. Euhedral crystals have no crystal faces, so they have no recognizable crystal form (FIGURE 3.1C). Most of the laboratory samples of minerals that you will analyze do not exhibit their crystal forms because they are small broken pieces of larger crystals. But whenever the form or system of crystals in a mineral sample can be detected, then it should be noted and used as evidence for mineral identification. Mineral Properties, Identification, and Uses ■ 77 Tetrahedron (4 faces) Needles (acicular) Twinned Pyramidal EQUANT Cube (6 faces) Bladed Dodecahedron (12 faces) Octahedron ((dipyramid)) Pyritohedron (12 faces) Dendritic Tabular (shaped like a book) Fibrous Radiating needles Rhombohedron (a leaning block with 6 faces, each a rhombus) Prismatic Wires Scalenohedrons Dipyramid prism Botryoidal (bubbly masses; radiating needles inside) FIGURE 3.4 Crystal forms and combinations. Crystal form is the geometric shape of a crystal, and is formed by intersecting flat outer surfaces called crystal faces. Combinations of two or more crystals can form patterns, shapes, or twins that also have names. Massive refers to a combination of mineral crystals so tightly inter-grown that their crystal forms cannot be seen in hand sample. Crystal Systems. Each specific crystal form can be classified into one of six crystal systems (FIGURE 3.5) according to the number, lengths, and angular relationships of imaginary geometric axes along which its crystal faces grew. The crystal systems comprise 32 classes of crystal forms, but only the common crystal forms are illustrated in FIGURE 3.5. Mineral Habit. A mineral’s habit is the characteristic crystal form(s) or combinations (clusters, coatings, twinned pairs) that it habitually makes under a given set of environmental conditions. Pyrite forms under a variety of environmental conditions so it has more than one habit. Its habit is cubes, pyritohedrons, octahedrons, or massive (FIGURE 3.4). Luster. A mineral’s luster is a description of how light reflects light from its surfaces. Luster is of two main types— metallic and nonmetallic—that vary in intensity from bright (very reflective, shiny, polished) to dull (not very reflective, not very shiny, not polished). For example, if you make a list of objects in your home that are made of metal (e.g., coins, knives, keys, jewelry, door hinges, aluminum foil), then you are already familiar with metallic luster. Yet the metallic objects can vary from bright (very reflective—like polished jewelry, the polished side of aluminum foil, or new coins) to dull (non-reflective—like unpolished jewelry or the unpolished side of aluminum foil). 78 ■ L A B O R AT O R Y 3 Metallic Luster. Minerals with a metallic luster (M) reflect light just like the metal objects in your home—they have opaque, reflective surfaces with a silvery, gold, brassy, or coppery sheen (FIGURES 3.2B, 3.6A, 3.7A). Nonmetallic Luster. All other minerals have a nonmetallic luster (NM)—a luster unlike that of the metal objects in your home (FIGURES 3.1, 3.2A, 3.3). The luster of nonmetallic minerals can also be described with the more specific terms below: ■ Vitreous—very reflective luster resembling freshly broken glass or a glossy photograph ■ Waxy—resembling the luster of a candle ■ Pearly—resembling the luster of a pearl ■ Earthy (dull)—lacking reflection, like dry soil ■ Greasy—resembling the luster of grease, oily Tarnish and Submetallic Luster. Most metallic minerals will normally tarnish (chemically weather) to a more dull nonmetallic luster, like copper coins. Notice how the exposed metallic copper crystals in FIGURE 3.6 and the galena crystals in FIGURE 3.2A have tarnished to a nonmetallic luster. Always observe freshly broken surfaces of a mineral (e.g., FIGURE 3.2B) to determine whether it has a metallic or nonmetallic luster. It is also useful to note a mineral’s luster on fresh versus tarnished Crystal Forms (Specific Geometric Shapes) and Their Classification into Six Systems Cube Octahedron (8 equilateral triangles) Rhombic dodecahedron (12 faces) Pyritohedron (12 faces) Equilateral tetrahedron Isometric (Cubic): Cubes and equidimensional shapes. Three axes intersect at 90° and are isometric (same in length). Tetragonal dipyramid (square cross section) Tetragonal dipyramid prisms (square cross section) Isosceles tetrahedrons (4 or 8 faces) Tetragonal: Like isometric but longer in one direction. Three axes intersect at 90° but only two are equal in length. Top Side Orthorhombic dipyramid (tetragonal bipyramid) Orthorhombic dipyramid prisms and tabular prisms 4- or 8-sided rectangular, squarish, or rhombic (diamond-shaped) horizontal cross sections Orthorhombic: Prisms and dipyramids with rhombic or rectangular cross sections. Three axes intersect at 90° but have different lengths. Scalenohedron (12 faces) Hexagonal prisms 3-sided prism Hexagonal dipyramid prism Rhombohedron 3-, 6-, or 12-sided horizontal cross sections, except for rhombohedrons (6 faces) Hexagonal: Rhombohedrons and mostly 3-, 6-, or 12-sided prisms and pyramids–three axes of equal length in one plane and perpendicular to a fourth axis of different length. Cross sections Monoclinic prisms Monoclinic tablet Monoclinic blade Monoclinic: Tablets (two very large faces like a book), prisms, and blades with six sides in diamond or parallelogram-shaped cross section.Three axes of unequal length, two in one plane and perpendicular to a third axis. Triclinic prisms and blades Triclinic: Tabular shapes, often not symmetrical from one side to the other. Three axes of different lengths and all inclined at each other (none are perpendicular to others). FIGURE 3.5 Crystal systems. Each specific crystal form can be classified into one of six crystal systems (major groups) according to the number, lengths, and angular relationships of imaginary geometric axes along which its crystal faces grew (red lines in the right-hand models of each system above). Only the common crystal forms of each class are illustrated and named above. Mineral Properties, Identification, and Uses ■ 79 C B A FIGURE 3.6 Native elements. The native elements are minerals composed of just one element, like gold nuggets. A. When freshly formed or broken, native copper (Cu, naturallyoccurring pure copper) has a reflective metallic luster like this freshly-minted copper coin. However, these dendritic clusters of native copper crystals have tarnished to nonmetallic dull brown (A) and/or green (B) colors. surfaces when possible. If you think that a mineral’s luster is submetallic, between metallic and nonmetallic, then it should be treated as metallic for identification purposes. Streak. Streak is the color of a mineral or other sub- stance after it has been ground to a fine powder (so fine that you cannot see the grains of powder). The easiest way to do this is simply by scratching the mineral back and forth across a hard surface such as concrete, or a square of unglazed porcelain (called a streak plate). The color of the mineral’s fine powder is its streak. Note that A: MINERAL CRYSTAL (CUBE) the brassy mineral in FIGURE 3.7 has a dark gray streak, but the reddish silver mineral has a red-brown streak. A mineral’s streak is usually similar even among all of that mineral’s varieties. If you encounter a mineral that is harder than the streak plate, it will scratch the streak plate and make a white streak of powder from the streak plate. The streak of such hard minerals can be determined by crushing a tiny piece of them with a hammer (if available). Otherwise, record the streak as unknown. Hardness (H). A mineral’s hardness is a measure of its resistance to scratching. A harder substance will scratch a softer one (FIGURE 3.8). German mineralogist Friedrich Mohs (1773–1839) developed a quantitative scale of relative mineral hardness on which the softest mineral (talc) has an arbitrary hardness of 1 and the hardest mineral (diamond) has an arbitrary hardness of 10. Highernumbered minerals will scratch lower-numbered minerals (e.g., diamond will scratch talc, but talc cannot scratch diamond). Mohs Scale of Hardness (FIGURE 3.9) is widely used by geologists and engineers. When identifying a mineral, you should mainly be able to distinguish minerals that are relatively hard (6.0 or higher on Mohs Scale) from minerals that are relatively soft (less than or equal to 5.5 on Mohs Scale). You can use common objects such as a glass plate (FIGURE 3.9), pocket knife, or steel masonry nail to make this distinction as follows. ■ Hard minerals: Will scratch glass; cannot be scratched with a knife blade or masonry nail. ■ Soft minerals: Will not scratch glass; can be scratched with a knife blade or masonry nail. You can determine a mineral’s hardness number on Mohs Scale by comparing the mineral to common objects B: FRAGMENT OF MINERAL CRYSTAL Streak plate Streak plate Color: brassy Streak: dark gray Luster: metallic (M) Color: reddish silver Streak: red-brown Luster: metallic (M) to nonmetallic (NM) FIGURE 3.7 Streak tests. Determine a mineral’s streak (color in powdered form) by scratching it across a streak plate with significant force, then blowing away larger pieces of the mineral to reveal the color of the powder making the streak. If you do not have a streak plate, then determine the streak color by crushing or scratching part of the sample to see the color of its powdered form. 80 ■ L A B O R AT O R Y 3 shown in FIGURE 3.9 or pieces of the minerals in Mohs Scale. Commercial hardness kits contain a set of all of the minerals in FIGURE 3.9 or a set of metal scribes of known hardnesses. When using such kits to make hardness comparisons, remember that the harder mineral/object is the one that scratches, and the softer mineral/object is the one that is scratched. Hardness test Glass plate FIGURE 3.8 Hardness test. You can test a mineral’s hardness (resistance to scratching) using a glass plate, which has a hardness of 5.5 on Mohs Scale of Hardness (FIGURE 3.9). Be sure the edges of the glass have been dulled. If not, then wrap the edges in masking tape or duct tape. Hold the glass plate firmly against a flat table top, then forcefully try to scratch the glass with the mineral sample. A mineral that scratches the glass is a hard mineral (i.e., harder than 5.5). A mineral that does not scratch the glass is a soft mineral (i.e., less than or equal to 5.5). Mohs Scale of Hardness* Cleavage and Fracture. Cleavage is the tendency of some minerals to break (cleave) along flat, parallel surfaces (cleavage planes) like the flat surfaces on broken pieces of galena (FIGURE 3.2B). Cleavage planes are surfaces of weak chemical bonding (attraction) between repeating, parallel layers of atoms in a crystal. Each different set of parallel cleavage planes is referred to as a cleavage direction. Cleavage can be described as excellent, good, or poor (FIGURE 3.10). An excellent cleavage direction reflects light in one direction from a set of obvious, large, flat, parallel surfaces. A good cleavage direction reflects light in one direction from a set of many small, obvious, flat, parallel surfaces. A poor cleavage direction reflects light from a set of small, flat, parallel surfaces that are difficult to detect. Some of the light is reflected in one direction from the small cleavage surfaces, but most of the light is scattered randomly by fracture surfaces separating the cleavage surfaces. Hardness of Some Common Objects (Harder objects scratch softer objects) 10 Diamond HARD 9 Corundum 8 Topaz 7 Quartz 6.5 Streak plate 6 Orthoclase Feldspar 5.5 Glass, Masonry nail, Knife blade 5 Apatite 4.5 Wire (iron) nail SOFT 4 Fluorite 3 Calcite 3.5 Brass (wood screw, washer) 2.9 Copper coin (penny) 2.5 Fingernail 2 Gypsum 1 Talc * A scale for measuring relative mineral hardness (resistance to scratching). FIGURE 3.9 Mohs Scale of Hardness (resistance to scratching). Hard minerals have a Mohs hardness number greater than 5.5, so they scratch glass and cannot be scratched with a knife blade or masonry (steel) nail. Soft minerals have a Mohs hardness number of 5.5 or less, so they do not scratch glass and are easily scratched by a knife blade or masonry (steel) nail. A mineral’s hardness number can be determined by comparing it to the hardness of other common objects or minerals of Mohs Scale of Hardness. Mineral Properties, Identification, and Uses ■ 81 Light rays A. Cleavage excellent or perfect (large, parallel, flat surfaces) Light rays Cleavage Direction. Cleavage planes are parallel surfaces of weak chemical bonding (attraction) between repeating parallel layers of atoms in a crystal, and more than one set of cleavage planes can be present in a crystal. Each different set has an orientation relative to the crystalline structure and is referred to as a cleavage direction (FIGURE 3.12). For example, muscovite (FIGURE 3.13) has one excellent cleavage direction and splits apart like pages of a book (book cleavage). Galena (FIGURE 3.2) breaks into small cubes and shapes made of cubes, so it has three cleavage directions developed at right angles to one another. This is called cubic cleavage (FIGURE 3.12). Cleavage Direction in Pyriboles. Minerals of the pyroxene (e.g., augite) and amphibole (e.g., hornblende) groups generally are both dark-colored (dark green to black), opaque, nonmetallic minerals that have two good B. Cleavage good or imperfect (small, parallel, flat, stair-like surfaces) Light rays A: Pure quartz (var. rock crystal) is colorless, transparent, nonmetalic, and has conchoidal fracture (like glass). C. Cleavage poor (a few small, flat surfaces difficult to detect) Light rays Conchoidal: smooth curved fracture surfaces, like glass Uneven: rough irregular fracture surfaces Hackly: breaks along jagged surfaces like broken metal Splintery: splinters like wood Fibrous: separates into soft fibers, like cloth D. Fractures (broken surfaces lacking cleavage planes) FIGURE 3.10 Recognizing cleavage and fracture. Illustrated cross sections of mineral samples to show degrees of development of cleavage—the tendency for a mineral to break along one or more sets of parallel, planar, reflective surfaces called cleavage planes. If a broken piece of a mineral crystal is rotated in bright light, its cleavage planes will be revealed by periodic flashes of light from one large, or many small, flat parallel surfaces. If no such reflective flashes of light occur, then the mineral sample has no cleavage. Fracture refers to any break in a mineral that does not occur along a cleavage plane. Therefore, fracture surfaces are normally not flat and they never occur in parallel sets. Fracture refers to any break in a mineral that does not occur along a cleavage plane. Therefore, fracture surfaces are normally not flat and they never occur in parallel sets. Fracture can be described as uneven (rough and irregular, like the milky quartz in FIGURE 3.11B), splintery (like splintered wood), or hackly (having jagged edges, like broken metal). Pure quartz (FIGURE 3.11A) and mineraloids like opal (FIGURE 3.3) tend to fracture like glass—along ribbed, smoothly curved surfaces called conchoidal fractures. 82 ■ L A B O R AT O R Y 3 (x1) (x1) B: Milky quartz forms when the quartz has microscopc fluid inclusions, usually water. It has an irregular (rough, uneven) fracture. FIGURE 3.11 Fracture in quartz—SiO2 (silicon dioxide). These hand samples are broken pieces of quartz mineral crystals so no crystal faces are present. Note the absence of cleavage and the presence of conchoidal (like glass) to uneven fracture. Number of Cleavages and Their Directions Name and Description of How the Mineral Breaks No cleavage (fractures only) No parallel broken surfaces; may have conchoidal fracture (like glass) Shape of Broken Pieces (cleavage directions are numbered) Illustration of Cleavage Directions None (no cleavage) Quartz Basal (book) cleavage 1 cleavage “Books” that split apart along flat sheets Prismatic cleavage 2 cleavages intersect at or near 90° 1 Muscovite, biotite, chlorite (micas) Orthoclase 90° (K-spar) 1 2 Elongated forms that fracture along short rectangular cross sections Plagioclase 86° & 94°, pyroxene (augite) 87° & 93° 2 cleavages do not intersect at 90° Prismatic cleavage 1 2 Elongated forms that fracture along short parallelogram cross sections Amphibole (hornblende) 56° & 124° 1 3 cleavages intersect at 90° Cubic cleavage 2 3 Shapes made of cubes and parts of cubes Halite, galena 3 cleavages do not intersect at 90° 1 Rhombohedral cleavage 3 2 Shapes made of rhombohedrons and parts of rhombohedrons Calcite and dolomite 75° & 105° 4 main cleavages intersect at 71° and 109° to form octahedrons, which split along hexagonshaped surfaces; may have secondary cleavages at 60° and 120° 6 cleavages intersect at 60° and 120° Octahedral cleavage 4 Shapes made of octahedrons and parts of octahedrons 3 1 2 Fluorite 2 Dodecahedral cleavage Shapes made of dodecahedrons and parts of dodecahedrons 1 3 5 4 6 Sphalerite FIGURE 3.12 Cleavage in minerals. Mineral Properties, Identification, and Uses ■ 83 Cleavage surface Notice how this muscovite mica splits apart into thin, transparent, flexible sheets along its excellent cleavage surfaces Cleavage surface Fracture surface Cleavage surface 87° Crystal Cleavage surface FIGURE 3.13 Cleavage in mica. Mica is a group of silicate minerals that form very reflective (vitreous) tabular crystals with one excellent cleavage direction. The crystals split easily into thin sheets, like pages of a book. This is called book cleavage. Muscovite mica is usually silvery brown in color. Biotite mica is always black. Crystal fragment A: Pyroxenes (like augite) have two prominent cleavage directions that intersect at nearly right angles (87° and 93°). They form prismatic crystals with a squarish cross section. The crystals break into blocky fragments. Cleavage surface cleavage directions. The two groups of minerals are sometimes difficult to distinguish, so some people identify them collectively as pyriboles. However, pyroxenes can be distinguished from amphiboles on the basis of their cleavage. The two cleavages of pyroxenes intersect at 87° and 93°, nearly at right angles (FIGURE 3.14A). The two cleavages of amphiboles intersect at angles of 56° and 124° (FIGURE 3.14B). These angles can be measured in hand samples using the cleavage goniometer from GeoTools Sheet 1 at the back of this manual. Notice how a green cleavage goniometer was used to measure angles between cleavage directions in FIGURE 3.14. Cleavage Direction in Feldspars. Feldspars have two excellent to good cleavage directions, plus uneven fracture (FIGURE 3.15). The cleavage goniometer from GeoTools Sheet 1 can be used to distinguish potassium feldspar (orthoclase) from plagioclase (FIGURE 3.15). Other Properties. There are additional mineral proper- ties, too numerous to review here. However, the following other properties are typical of specific minerals or mineral groups: Tenacity is the manner in which a substance resists breakage. Terms used to describe mineral tenacity include brittle (shatters like glass), malleable (like modeling clay or gold; can be hammered or bent permanently into new shapes), elastic or flexible (like a plastic comb; bends but returns to its original shape), and sectile (can be carved with a knife). Reaction to acid differs among minerals. Cool, dilute hydrochloric acid (1–3% HCl) applied from a dropper bottle is a common “acid test.” All of the so-called carbonate minerals (minerals with a chemical composition 84 ■ L A B O R AT O R Y 3 Cleavage surface Crystal Crystal fragment Fracture surface 56° B: Amphiboles (like hornblende) have two prominent cleavage directions that intersect at 56° and 124°. They form more blade-like crystals with a six-sided diamond-shaped cross section and break into blade-like fragments. FIGURE 3.14 Cleavage in pyroxenes and amphiboles. Pyroxenes and amphiboles are two groups of dark colored silicate minerals with many similar properties. The main feature that distinguishes them is their cleavage. including carbonate, CO3) will effervesce (“fizz”) when a drop of such dilute HCl is applied to one of their freshly exposed surfaces (FIGURE 3.16). Calcite 1CaCO32 is the most commonly encountered carbonate mineral and effervesces in the acid test. Dolomite 3Ca,Mg1CO3224 is Plagioclase Pink K-feldspar (orthoclase) Fracture surfaces 86° 90° Right-angle cleavage Cleavage planes with no striations A. Plagioclase Cleavage plane with parallel, closely spaced striations Fracture surfaces at broken ends of crystals Cleavage plane with subparallel color variation bands from exsolution lamellae Cleavage plane with parallel, closely spaced striations 94° White K-feldspar (orthoclase) 90° Right-angle cleavage B. Pink K-feldspar (orthoclase) Cleavage surface with striations C. Rock comprised of plagioclase crystals FIGURE 3.15 Common feldspars. Note how the cleavage goniometer can be used to distinguish potassium feldspar (K-spar, orthoclase) from plagioclase. The K-spar or orthoclase (Greek, ortho—right angle and clase—break) has perfect right-angle (90º) cleavage. Plagioclase (Greek, plagio—oblique angle and clase—break) does not. A. Plagioclase often exhibits hairline striations on some of its cleavage surfaces. They are caused by twinning: microscopic intergrowths between symmetrically-paired microcrystalline portions of the larger crystal. B. K-par (orthoclase) crystals may have intergrowths of thin, discontinuous, exsolution lamellae. They are actually microscopic layers of plagioclase that form as the K-spar cools, like fat separates from soup when it is refrigerated. C. Hand sample of a rock that is an aggregate of intergrown plagioclase mineral crystals. Individual mineral crystals are discernible within the rock, particularly the cleavage surfaces that have characteristic hairline striations. another carbonate mineral that resembles calcite, but it will fizz in dilute HCl only if the mineral is first powdered. (It can be powdered for this test by simply scratching the mineral’s surface with the tip of a rock pick, pocket knife, or nail.) If HCl is not available, then undiluted vinegar can be used for the acid test. It contains acetic acid (but the effervescence will be much less violent). Striations are straight “hairline” grooves on the cleavage surfaces or crystal faces of some minerals. This can be helpful in mineral identification. For example, you can use the striations of plagioclase feldspar (FIGURE 3.15A) to distinguish it from potassium feldspar (K-feldspar, FIGURE 3.15B). Plagioclase feldspar has faint hairline striations on surfaces of one of its two cleavage directions. In contrast, K- feldspar (orthoclase) sometimes has internal exsolution lamellae, which are faint streaks of plagioclase that grew inside of it. Magnetism influences some minerals, such as magnetite. The test is simple: check to see if the mineral is attracted to a magnet. Lodestone is a variety of magnetite that is itself a natural magnet. It will attract steel paperclips. Some other minerals may also be weakly attracted to a magnet (e.g., hematite, bornite, and pyrrhotite). Specific Gravity (SG). Density is a measure of an object’s mass (weighed in grams, g) divided by its volume (in cubic centimeters, cm3). Specific gravity is the ratio of the density of a substance divided by the density of water. Since water has a density of 1 g>cm3 and the units cancel out, specific gravity is the same number as density but without any units. For example, the mineral quartz has a density of 2.65 g>cm3 so its specific gravity is 2.65 (i.e., SG = 2.65). Hefting is an easy way to judge the specific gravity of one mineral relative to another. This is done by holding a piece of the first mineral in one hand and holding an equal-sized piece of the second mineral in your other hand. Feel the difference in weight between the two samples (i.e., heft the samples). The sample that feels heavier has a higher specific gravity than the other. Most metallic minerals have higher specific gravities than nonmetallic minerals. Mineral Properties, Identification, and Uses ■ 85 Why Are Density and Specific Gravity Important? x1 FIGURE 3.16 Acid test. Place a drop of weak hydrochloric acid (HCl) on the sample. If it effervesces (reacts, bubbles), then it is a carbonate (CO3- containing) mineral. Please wipe the sample dry with a paper towel after doing this test! Note that the mineral in this example occurs in several different colors and can be scratched by a wire (iron) nail. The yellow sample is a crystal of this mineral, but the other samples are broken pieces of crystals that reveal the mineral’s characteristic cleavage angles. ACTIVITY 3.3 Determining Specific Gravity (SG) THINK How and why do people study About It minerals? OBJECTIVE Measure the volume and mass of minerals, calculate their specific gravities, and use the results to identify them. PROCEDURES 1. Before you begin, read the following background information. Your instructor will provide laboratory equipment, but this is what you will need to bring to lab: ___ Activity 3.3 Worksheet (p. 104) and pencil ___ calculator 2. Then follow your instructor’s directions about where to obtain laboratory equipment and mineral samples, how to work safely, and how to complete the worksheet. 86 ■ L A B O R AT O R Y 3 Have you ever considered buying silver coins as an investment? If so, then you should be wary of deceptive sales. For example, there have been reports of less valuable silver-plated copper coins marketed as pure silver coins. Copper has a specific gravity of 8.94, which is very close to silver’s specific gravity of 9.32. So, even experienced buyers cannot tell a solid silver coin from a silver-plated copper coin just by hefting it to approximate its specific gravity. They must determine the coin’s exact specific gravity as one method of ensuring its authenticity. Mineral identification is also aided by knowledge of specific gravity. If you heft same-sized pieces of the minerals galena (lead sulfide, an ore of lead) and quartz, you can easily tell that one has a much higher specific gravity than the other. But the difference in specific gravities of different minerals is not always so obvious. In this activity you will learn how to measure the volume and mass of mineral samples, calculate their specific gravities, and use the results to identify them. Before you begin, read the following background information and be sure you have a pencil, eraser, and Worksheet 3.3 (p. 102). Then complete the activity and Worksheet 3.3. How to Determine Volume. Recall that volume is the amount of space that an object takes up. Most mineral samples have odd shapes, so their volumes cannot be calculated from linear measurements. Their volumes must be determined by measuring the volume of water they displace. This is done in the laboratory with a graduated cylinder (FIGURE 3.17), an instrument used to measure volumes of fluid (fluid volume). Most graduated cylinders are graduated in metric units called milliliters (mL or ml), which are thousandths of a liter. You should also note that 1 mL (1 ml) of fluid volume is exactly the same as 1 cm3 of linear volume. Procedures for determining the volume of a mineral sample are provided in FIGURE 3.17. Note that when you pour water into a glass graduated cylinder, the surface of the liquid is usually a curved meniscus, and the volume is read at the bottom of its concave surface. In most plastic graduated cylinders, however, there is no meniscus. The water level is flat and easy to read. If you slide a mineral sample into a graduated cylinder full of water (so no water splashes out), then it takes up space previously occupied by water at the bottom of the graduated cylinder. This displaced water has nowhere to go except higher into the graduated cylinder. Therefore, the volume of the mineral sample is exactly the same as the volume of fluid (water) that it displaces. How to Determine Mass. Earth materials do not just take up space (volume). They also have a mass of atoms that can be weighed. You will use a gram balance to measure the mass of materials (by determining their weight under the pull of Earth’s gravity). The gram (g) is the basic unit of mass in the metric system, but instruments used to measure grams vary from triple-beam balances to spring scales to digital balances (page viii). Consult with your laboratory instructor or other students to be sure that you understand how to read the gram balance provided in your laboratory. WATER DISPLACEMENT METHOD FOR DETERMINING VOLUME OF A MINERAL SAMPLE mL 10 Written mL or ml mL 10 9 9 8 8 7 7 6 5 C. Volume of water is 2.8 mL 5.0 mL 6 5 4 3 7.8 mL 4 Mineral sample 3 2 2 1 1 How to Calculate Density and Specific Gravity. Every material has a mass that can be weighed and a volume of space that it occupies. However, the relationship between a material’s mass and volume tends to vary from one kind of material to another. For example, a bucket of rocks has much greater mass than an equal-sized bucket of air. Therefore a useful way to describe an object is to determine its mass per unit of volume, called density. Per refers to division, as in miles per hour (distance divided by time). So density is the measure of an object’s mass divided by its volume (density = mass ÷ volume). Scientists and mathematicians use the Greek character rho (r) to represent density. Also, the gram (g) is the basic metric unit of mass, and the cubic centimeter is the basic unit of metric volume (cm3), so density (r) is usually expressed in grams per cubic centimeter (g/cm3). For example: Mineral sample weighs 44.0 grams Mineral sample takes up 11.0 ml of volume A. Starting volume of water B. Ending volume of water = PROCEDURES A. Place water in the bottom of a graduated cylinder. Add enough water to be able to totally immerse the mineral sample. It is also helpful to use a dropper bottle or wash bottle and bring the volume of water (before adding the mineral sample) up to an exact graduation mark like the 5.0 mL mark above. Record this starting volume of water. 44.0 g 11.0 cm3 = 4.00 g>cm3 = r Specific gravity (SG) is the ratio of the density of a substance divided by the density of water. Since water has a density of 1 g>cm3 and the units cancel out, specific gravity is the same number as density but without any units. In the example above, the specific gravity of the mineral sample would be 4.00 (i.e., SG = 4.00). The mineral quartz has a density of 2.65 g/cm3 so its specific gravity is 2.65 (i.e., SG = 2.65). B. Carefully slide the mineral sample down into the same graduated cylinder, and record the ending volume of the water (7.8 mL in the above example). C. Subtract the starting volume of water from the ending volume of water to obtain the displaced volume of water. In the above example: 7.8 mL – 5.0 mL = 2.8 mL (2.8 mL is the same as 2.8 cm3 ). This volume of displaced water is the volume of the mineral sample. FIGURE 3.17 How to determine volume of a mineral sample. Calculating Density and Specific Gravity— The Math You Need You can learn more about calculating density and specific gravity at this site featuring The Math You Need, When You Need It math tutorials for students in introductory geoscience courses: http://serc.carleton.edu/ mathyouneed/density/index.html Mineral Properties, Identification, and Uses ■ 87 ACTIVITY 3.4 Mineral Identification and Uses THINK How and why do people study About It minerals? How do you personally depend on minerals and elements extracted from them? OBJECTIVE Identify common minerals on the basis of their properties and assess how you depend on them. PROCEDURES 1. Before you begin, read the introduction and mineral identification procedures below. Your instructor will provide laboratory equipment, but this is what you will need to bring to lab: ___ Activity 3.4 Worksheets (pp. 105–108) and pencil 2. To complete the activity, follow your instructor’s directions about where to obtain a set of mineral analysis tools and mineral samples and any additional procedures for completing Worksheet 3.4 (which you will also need for Activity 3.5). 3. When you have completed your worksheets, reflect on how you depend on each of the minerals that you identified. What did you learn about how you depend on minerals? Be prepared to discuss this question and your mineral identifications. Save your Activity 3.4 worksheets to complete Activity 3.5. Introduction You are expected to learn how to identify common minerals on the basis of their properties and assess how you depend on them. The ability to identify minerals is one of the most fundamental skills of an Earth scientist. It also is fundamental to identifying rocks, for you must first identify the minerals comprising them. Only after minerals and rocks have been identified can their origin, classification, and alteration be adequately understood. Mineral identification is based on your ability to describe mineral properties using identification charts (FIGURES 3.18–3.20) and a Mineral Database (FIGURE 3.21). The database also lists the chemical composition and some common uses for each mineral. Some minerals, like halite (table salt) and gemstones are used in their natural state. Others are valuable as ores—materials from which specific chemical elements (usually metals) can be extracted at a profit. 88 ■ L A B O R AT O R Y 3 Mineral Identification Procedures Obtain a set of mineral samples and analysis tools according to your instructor’s instructions. For each sample, fill in the Activity 3.3 tear-out worksheet using the procedures provided below. 1. Record the sample number or letter. 2. Determine and record the mineral’s luster as metallic (M) or nonmetallic (NM) A. Metallic (M): mineral is opaque, looks like metal or sort of like metal) B. Nonmetallic (NM): e.g., vitreous (glassy, glossy reflection), waxy, pearly, earthy/dull, greasy 3. Determine and record the mineral’s hardness (FIGS. 3.8, 3.9): give a hardness range, if possible. 4. Determine and record the mineral’s cleavage (if present, FIGURES. 3.10–3.16) and fracture (if present, FIGURE 3.10). For cleavage, determine number of cleavage directions or name, if possible (FIGURE 3.12). 5. Determine and record the mineral’s color (fresh surface) and streak (using a streak plate). Minerals harder than 6.5 will scratch the streak plate, so no streak can be determined for them. 6. Determine and record other notable properties like these: A. What is the mineral’s tenacity: brittle, elastic, malleable, or sectile (can be carved with a knife)? B. Does the mineral sample display magnetic attraction (strongly or weakly)? C. Does the mineral sample display a reaction with acid (dilute HCl)? D. If crystals are visible, then what is their crystal form? E. Does the mineral sample have striations on cleavage surfaces or crystal faces or exsolution lamellae (FIGURE 3.15)? F. Estimate specific gravity (SG) as low, intermediate, or high. G. Does the mineral sample have any unique diagnostic properties like smell when scratched or during acid test? 7. Use mineral identification figures to identify the name of the mineral. A. If the mineral is opaque and metallic or submetallic, follow steps 1–5 in FIGURE 3.18. B. If the mineral is light colored and nonmetallic, then follow steps 1–4 in FIGURE 3.19. C. If the mineral is dark colored and nonmetallic, then follow steps 1–4 in FIGURE 3.20. 8. Use the Mineral Database (FIGURE 3.21) and FIGURE 3.22 to determine and record the mineral’s chemical composition and help you determine how you personally depend on the mineral (including commodities refined from it). For more information about specific minerals or elements, you can refer to the U.S. Geological Survey’s Mineral Commodity Summaries (http://minerals.usgs.gov/ minerals/pubs/mcs/). ACTIVITY 3.5 The Mineral Dependency Crisis THINK How do you personally depend on About It minerals and elements extracted from them? How sustainable is your dependency on minerals and elements extracted from them? OBJECTIVE Evaluate your personal and U.S. dependency on minerals. PROCEDURES 1. Before you begin, read the background information below and on page 99. Your instructor will provide laboratory equipment, but this is what you will need to bring to lab: ___ Activity 3.5 Worksheet (p. 109) and pencil ___ Activity 3.4 Worksheets that you already completed 2. Then refer to FIGURE 3.22, and follow your instructor’s directions about how to complete the Activity 3.5 worksheet. goggles, missile systems, and medical equipment. China currently produces nearly all of the world’s supply of rare earth elements, and the United States produces almost none. This has created what is widely known as the “rare earth crisis,” and a shortage of rare earth elements used to make fluorescent light bulbs has become widely known as the “phosphor crisis.” Yet the United States also relies on foreign supplies of many other minerals and elements extracted from them. Has the United States entered an unsustainable level of mineral dependency? U.S. Net Import Reliance on Non-fuel Mineral Resources Commodities are natural materials that people buy and sell, because they are required to sustain our wants and needs. Three classes are: agricultural products, energy resources, and non-fuel mineral resources. The nonfuel mineral resources include rocks, minerals used in their unrefined state or as ore from which specific elements can be profitably refined, and chemical elements extracted from ores. The U.S. Geological Survey (USGS) has determined that the United States was the world’s largest user of non-fuel mineral resources in 2012 (about 12,000 pounds, or 11.3 metric tons, per person each year). To sustain its needs, the U.S. imported some of the minerals (and elements already extracted from them) that it needed. FIGURE 3.22 shows the 2012 U.S. net import reliance (expressed as a percent) on some selected minerals and elements refined from them. The United States exports some of the same non-fuel mineral resources that it imports, so net import reliance is the total of U.S. production and imports, minus the percentage of exports. A net import reliance of 80% means that 80% of the resource is imported. FIGURE 3.22 does not include all of the rare earth elements. Also not shown are minerals and elements for which the U.S. is less than 5% import reliant (or a net exporter). USGS Mineral Resources Data System (MRDS) Mineral Dependency Did you know that some of the minerals used to make your cell phone and fluorescent light bulbs are quite rare nonrenewable resources? Many high-tech products depend on such nonrenewable mineral resources, yet many are either not mined within the United States or are mined here only in small quantities. The locations where they can be economically extracted in the United States have already been mined or are too small to be developed. Of particular concern are minerals mined as ores for rare earth elements, a group of 17 elements used in products like fluorescent light bulbs, flat screen televisions, cell phones, computers, solar panels, wind turbines, hybrid cars, cameras, DVDs, rechargeable batteries, magnets, medical equipment, night-vision Recall that commodities are natural materials that people buy and sell, because they are required to sustain our wants and needs. Three classes are: agricultural products, energy resources, and non-fuel mineral resources. The U.S. Geological Survey (USGS) divides the non-fuel mineral resources into two groups. Nonmetallic mineral resources are mostly rocks made of unrefined minerals (such as rock salt) and rocks (gravel, granite, marble). Metallic mineral resources are ores (rocks or minerals from which chemicals, usually metals, can be extracted at a profit) and chemical elements that have already been extracted from ore minerals. The USGS Mineral Resources Data System (MRDS) is a global database of both kinds of mineral resources and where they have been found and/or processed. Mineral Properties, Identification, and Uses ■ 89 METALLIC AND SUBMETALLIC (M) MINERAL IDENTIFICATION STEP 1: What is the mineral’s hardness? STEP 2: Does the mineral have cleavage? HARD (H > 5.5) Scratches glass STEP 3: What is the mineral’s streak? Pyrite Silvery dark gray to black; Tarnishes gray or rusty yellow-brown; Strongly attracted to a magnet and may be magnetized; H 6–6.5; Crystals: octahedrons Magnetite Yellow-brown Color submetallic silvery brown; Tarnishes to dull and earthy yellow-brown to brown rust colors; H 1–5.5; More commonly occurs in its nonmetallic yellow to brown forms (H 1–5) Limonite Brown Color silvery black to black; Tarnishes gray to black; H 5.5–6; May be weakly attracted to a magnet; Crystals: octahedrons Chromite Red to red-brown Color steel gray, reddish-silver, to glittery bright silver (var. specular); Both metallic varieties have the characteristic red-brown streak; May be attracted to a magnet; H 5–6; Also occurs in nonmetallic, dull to earthy, red to red-brown forms Dark gray to black Color bright silvery gray; Tarnishes dull gray; Brittle: breaks into cubes and shapes made of cubes; H 2.5; Crystals: cubes or octahedrons; Feels heavy for its size because of high specific gravity Galena White to pale yellow-brown Color silvery yellow-brown, silvery red, or black with submetallic to resinous luster; Tarnishes brown or black; H 3.5–4.0; smells like rotten eggs when scratched, powdered, or in acid test Sphalerite Color bright silvery gold; Tarnishes bronze brown brassy gold, or iridescent blue-green and red; H 3.5–4.0; Brittle; uneven fracture; Crystals: tetrahedrons Chalcopyrite Color characteristically brownish-bronze; Tarnishes bright iridescent purple, blue, and/or red, giving It its nickname “peacock ore”; May be weakly attracted to a magnet; H 3; Usually massive, rare as cubes or dodecahedrons Bornite Color opaque brassy to brown-bronze; Tarnishes dull brown, may have faint iridescent colors; Fracture uneven to conchoidal; No cleavage; Attracted to a magnet; H 3.5–4.5; Usually massive or masses of tiny crystals; Resembles chalcopyrite, which is softer and not attracted to a magnet Pyrrhotite Color dark silvery gray to black; Can be scratched with your fingernail; Easily rubs off on your fingers and clothes, making them gray; H 1–2 Graphite Yellow-brown Metallic or silky submetallic luster, Color dark brown, gray, or black; H 5–5.5; Forms layers of radiating microscopic crystals and botryoidal masses Goethite Copper Color copper; Tarnishes dull brown or green; H 2.5–3.0; Malleable and sectile; Hackly fracture; Usually forms dendritic masses or nuggets Copper (native copper) Gold Color yellow gold; Does not tarnish; Malleable and sectile; H 2.5–3.0; Forms odd-shaped masses, nuggets, or dendritic forms Gold (native gold) Silvery white Color silvery white to gray; Tarnishes gray to black; H 2.5–3.0; Malleable and sectile; Forms dendritic masses, nuggets, or curled wires Silver (native silver) Not scratched by masonry nail or knife blade HARD or SOFT Cleavage good to excellent SOFT (H < 5.5) Dark gray to black Does not scratch glass Scratched by masonry nail or knife blade STEP 5: Mineral name. Find out more about it in the mineral database (Fig.3.21). Color silvery gold; Tarnishes brown; H 6–6.5; Brittle; conchoidal to uneven fracture; Crystals: cubes (may be striated), pyritohedrons, or octahedrons; Distinguished from chalcopyrite, which is soft Dark gray to black Cleavage absent, poor, or not visible STEP 4: Match the mineral’s physical properties to other characteristic properties below. Cleavage absent, poor, or not visible Hematite FIGURE 3.18 Identification chart for opaque minerals with metallic or submetallic luster (M) on freshly broken surfaces. 90 ■ L A B O R AT O R Y 3 DARK TO MEDIUM-COLORED NONMETALLIC (NM) MINERAL IDENTIFICATION STEP 1: What is the mineral’s hardness? STEP 2: What is the mineral’s cleavage? STEP 4: Find mineral name(s) and check the mineral database for additional properties (Figure 3.21). STEP 3: Compare the mineral’s physical properties to other distinctive properties below. Translucent to opaque dark gray; blue-gray, or black; May have silvery iridescence; 2 cleavages at nearly 90° and with striations; H 6 Plagioclase feldspar Translucent to opaque brown, gray, green, or red; 2 cleavages at nearly right angles; Exsolution lamellae; H 6 Potassium feldspar (K-spar) Green to black; Vitreous luster; H 5.5–6.0; 2 cleavages at about 124° and 56° plus uneven fracture; Usually forms long blades and masses of needle-like crystals Actinolite (amphibole) Dark gray to black; Vitreous luster; H 5.5–6.0; 2 cleavages at about 124° and 56° plus uneven fracture; Forms long crystals that break into blade-like fragments Hornblende (amphibole) HARD (H > 5.5) Dark green to black; Dull to vitreous luster; H 5.5–6.0; two cleavages at nearly right angles (93° and 87°) plus uneven fracture; Forms short crystals with squarish cross sections; Breaks into blocky fragments Augite (pyroxene) Scratches glass Transparent or translucent gray, brown, or purple; Greasy luster; Massive or hexagonal prisms and pyramids; H 7 Quartz Smoky quartz (black/brown var.), Amethyst (purple var.) Not scratched by masonry nail or knife blade Gray, black, or colored (dark red, blue, brown) hexagonal prisms with flat striated ends; H 9 Corundum Emery (black impure var.), Ruby (red var.) Sapphire (blue var.) Opaque red-brown or brown; Luster waxy; Cryptocrystalline; H 7 Transparent to translucent dark red to black; Equant (dodecahedron) crystal form or massive; H 7 Jasper (variety of quartz) Garnet Opaque gray; Luster waxy; Cryptocrystalline; H 7 Opaque black; Luster waxy; Cryptocrystalline; H 7 Black or dark green; Long striated prisms; H 7–7.5 Olive green, Transparent or translucent; No cleavage; Usually has many cracks and conchoidal to uneven fracture; Single crystals or masses of tiny crystals resembling green granulated sugar or aquarium gravel; The crystals have vitreous (glassy) luster Chert (gray variety of quartz) Flint (black variety of quartz) Tourmaline Olivine Opaque dark gray to black; Tarnishes gray to rusty yellow-brown; Cleavage absent; Strongly attracted to a magnet; May be magnetized; H 6–6.5 Magnetite Opaque green; Poor cleavage; H 6–7 Opaque brown prisms and cross-shaped twins; H 7 Yellow-brown, brown, or black; vitreous to resinous luster (may also be submetallic); Dodecahedral cleavage; H 3.5–4.0; Rotten egg smell when scratched or powdered Epidote Staurolite Sphalerite Purple cubes or octahedrons; Octahedral cleavage; H 4 Black short opaque prisms; Splits easily along 1 excellent cleavage into thin sheets; H 2.5–3 Fluorite Biotite (black mica) Green short opaque prisms; Splits easily along 1 excellent cleavage into thin sheets; H 2–3 Chlorite Opaque rusty brown or yellow-brown; Massive and amorphous; Yellow-brown streak; H 1–5.5 Limonite Rusty brown to red-brown, may have shades of tan or white; Earthy and opaque; Contains pea-sized spheres that are laminated internally; H 1–5; Pale brown streak Bauxite Deep blue; Crusts, small crystals, or massive; Light blue streak; H 3.5–4 Azurite Opaque green or gray-green; Dull or silky masses or asbestos; White streak; H 2–5 Serpentine Opaque green in laminated crusts or massive; Streak pale green; Effervesces in dilute HCI; H 3.5–4 Malachite Translucent or opaque dark green; Can be scratched with your fingernail; Feels greasy or soapy; H 1 Talc Transparent or translucent green, brown, blue, or purple; Brittle hexagonal prisms; Conchoidal fracture; H 5 Apatite Opaque earthy brick red to dull red-gray, or gray; H 1.5–5; Red-brown streak; Magnet may attract the gray forms Hematite Cleavage excellent or good Cleavage absent, poor, or not visible Cleavage excellent or good SOFT (H < 5.5) Does not scratch glass Scratched by masonry nail or knife blade Cleavage absent, poor, or not visible FIGURE 3.19 Identification chart for dark to medium-colored minerals with nonmetallic (NM) luster on freshly broken surfaces. Mineral Properties, Identification, and Uses ■ 91 LIGHT-COLORED NONMETALLIC (NM) MINERAL IDENTIFICATION STEP 1: What is the mineral’s hardness? STEP 2: What is the mineral’s cleavage? STEP 3: Compare the mineral’s physical properties to other distinctive properties below. STEP 4: Find mineral name(s) and check the mineral database for additional properties (Figure 3.21). White or pale gray; 2 good cleavages at nearly 90° plus uneven fracture; May have striations; H 6 Plagioclase feldspar Orange, pink, pale brown, green, or white; H 6; 2 good cleavages at 90° plus uneven fracture; exsolution lamellae Potassium feldspar Pale brown, white, or gray; Long slender prisms; 1 excellent cleavage plus fracture surfaces; H 6–7 Sillimanite Blue, very pale green, white, or gray; Crystals are blades; H 4–7 Kyanite Gray, white, or colored (dark red, blue, brown) hexagonal prisms with flat striated ends; H 9 Corundum vars. ruby (red), sapphire (blue) Colorless, white, gray, or other colors; Greasy luster; Massive or hexagonal prisms and pyramids; Transparent or translucent; H 7 Quartz: vars. rose (pink), rock crystal (colorless), milky (white), citrine (amber) Opaque gray or white; Luster waxy; H 7 Chert (variety of quartz) Colorless, white, yellow, light brown, or pastel colors; Translucent or opaque; Laminated or massive; Cryptocrystalline; Luster waxy; H 7 Chalcedony (variety of quartz) Pale green to yellow; Transparent or translucent; H 7; No cleavage; Usually has many cracks and conchoidal to uneven fracture; Single crystals or masses of tiny crystals resembling green or yellow granulated sugar or aquarium gravel; Crystals vitreous (glassy) Olivine Colorless, white, yellow, green, pink, or brown; 3 excellent cleavages; Breaks into rhombohedrons; Effervesces in dilute HCI; H 3 Calcite Colorless, white, gray, creme, or pink; 3 excellent cleavages; Breaks into rhombohedrons; Effervesces in dilute HCI only if powdered; H 3.5–4 Dolomite Colorless or white with tints of brown, yellow, blue, black; Short tabular crystals and roses; Very heavy; H 3–3.5 Barite Transparent, colorless to white; H 2, easily scratched with your fingernail; White streak; Blade-like crystals or massive Gypsum var. selenite Colorless, white, gray, or pale green, yellow, or red; Spheres of radiating needles; Luster silky; H 5–5.5 Natrolite (zeolite) Colorless, white, yellow, blue, brown, or red; Cubic crystals; Breaks into cubes; Salty taste; H 2.5 Halite SOFT (H < 5.5) Colorless, purple, blue, gray, green, yellow; Cubes with octahedral cleavage; H 4 Fluorite Does not scratch glass Colorless, yellow, brown, or red-brown; Short opaque prisms; Splits along 1 excellent cleavage into thin flexible transparent sheets; H 2–2.5 Muscovite (white mica) White, gray or yellow; Earthy to pearly; massive form; H 2, easily scratched with your fingernail; White streak Gypsum var. alabaster White to gray; Fibrous form with silky or satiny luster; H 2, easily scratched with your fingernail Gypsum var. satin spar Yellow crystals or earthy masses; Luster greasy; H 1.5–2.5; Smells like rotten eggs when powdered Sulfur (Native sulfur) Opaque pale blue to blue-green; Conchoidal fracture; H 2-4; Massive or amorphous earthy crusts; Very light blue streak Chrysocolla Opaque green, yellow, or gray; Dull or silky masses or asbestos; White streak; H 2–5 Serpentine Opaque white, gray, green, or brown; Can be scratched with fingernail; Greasy or soapy feel; H 1 Talc Opaque earthy white to very light brown masses of “white clay”; H 1–2; Powdery to greasy feel Kaolinite Mostly pale brown to tan or white; Earthy and opaque; Contains pea-sized spheres that are laminated internally; H 1–5; Pale brown to white streak Bauxite Colorless to white, orange, yellow, blue, gray, green, or red; May have internal play of colors; H 5.0–5.5; Amorphous; Often has many cracks; Conchoidal fracture Opal Colorless or pale green, brown, blue, white, or purple; Brittle hexagonal prisms; Conchoidal fracture; H 5 Apatite Cleavage excellent or good HARD (H > 5.5) Scratches glass Not scratched by masonry nail or knife blade Cleavage absent, poor, or not visible Cleavage excellent or good Scratched by masonry nail or knife blade Cleavage absent, poor, or not visible FIGURE 3.20 Identification chart for light-colored minerals with nonmetallic (NM) luster on freshly broken surfaces. 92 ■ L A B O R AT O R Y 3 MINERAL DATABASE (Alphabetical Listing) Mineral ACTINOLITE (amphibole) Luster and Hardness Crystal System Nonmetallic (NM) 5.5–6 Distinctive Properties Streak White Monoclinic Some Uses Color dark green or pale green; Forms needles, prisms, and asbestose fibers; Good cleavage at 56° and 124°; SG = 3.1 Green gem varieties are the gemstone “nephrite jade”; asbestos products Color pale or dark green, brown, blue, white, or purple; Sometimes colorless; Transparent or opaque; Brittle; Conchoidal fracture; Forms hexagonal prisms; SG = 3.1–3.4 Used mostly to make fertilizer, pesticides; Transparent varieties sold as gemstones AMPHIBOLE: See HORNEBLENDE and ACTINOLITE APATITE Ca5F(PO4)3 calcium fluorophosphate Nonmetallic (NM) 5 White Hexagonal ASBESTOS: fibrous varieties of AMPHIBOLE and SERPENTINE AUGITE (pyroxene) calcium ferromagnesian silicate Nonmetallic (NM) AZURITE Cu3(CO3)2(OH)2 copper carbonate hydroxide Nonmetallic (NM) 5.5–6 White to pale gray Color dark green to brown or black; Forms short, 8-sided prisms; Two good cleavages that intersect at 87° and 93° (nearly right angles); SG = 3.2–3.5 Ore of lithium, used to make lithium batteries, ovenware glazes, high temperature grease, and to treat depression 3.5–4 Light blue Color a distinctive deep blue; Forms crusts of small crystals, opaque earthy masses, or short and long prisms; Brittle; Effervesces in dilute HCI; SG = 3.7–3.8 Ore of copper used to make pipes, electrical wire, coins, ammunition, bronze, brass; added to vitamin pills for healthy hair and skin; Gemstone 3–3.5 White Colorless to white, with tints of brown, yellow, blue, or red; Forms short tabular crystals and rose-shaped masses (Barite roses); Brittle; Cleavage good to excellent; Very heavy, SG = 4.3–4.6 Ore of barium, used to harden rubber, make fluorescent lamp electrodes, and in fluids used to drill oil/gas wells 1–3 White Brown earthy rock with shades of gray, white, and yellow; Amorphous; Often contains rounded pea-sized structures with laminations; SG = 2.0–3.0 Ore of aluminum used to make cans, foil, airplanes, solar panels; Ore of gallium used to make LED bulbs and liquid crystal displays in cell phones, computers, flat screen televisions Gray-brown to white Color black, green-black, or brown-black; Cleavage excellent; Forms very short prisms that split easily into very thin, flexible sheets; SG = 2.7–3.1 Used for fire-resistant tiles, rubber, paint 3 Dark gray to black Color brownish bronze; Tarnishes bright purple, blue, and/or red; May be weakly attracted to a magnet; H 3; Cleavage absent or poor; Forms dense brittle masses; Rarely forms crystals Ore of copper, used to make pipes, electrical wire, coins, ammunition, bronze, brass; added to vitamin pills for healthy hair and skin 3 White Usually colorless, white, or yellow, but may be green, brown, or pink; Opaque or transparent; Excellent cleavage in 3 directions not at 90°; Forms prisms, rhombohedrons, or scalenohedrons that break into rhombohedrons; Effervesces in dilute HCI; SG = 2.7 Used to make antacid tablets, fertilizer, cement; Ore of calcium 7 White* Colorless, white, yellow, light brown, or other pastel colors in laminations; Often translucent; Conchoidal fracture; Luster waxy; Cryptocrystalline; SG = 2.5–2.8 Used as an abrasive; Used to make glass, gemstones (agate, chrysoprase) Monoclinic Monoclinic BARITE BaSO4 barium sulfate Nonmetallic (NM) Orthorhombic BAUXITE Mixture of aluminum hydroxides Nonmetallic (NM) No visible crystals Nonmetallic BIOTITE MICA (NM) ferromagnesian potassium, hydrous Monoclinic aluminum silicate K(Mg,Fe)3 (Al,Si3O10)(OH,F)2 BORNITE Cu5FeS4 copper-iron sulfide Metallic (M) 2.5–3 Isometric CALCITE CaCO3 calcium carbonate Nonmetallic (NM) Hexagonal CHALCEDONY SiO2 cryptocrystalline quartz Nonmetallic (NM) No visible crystals *Streak cannot be determined with a streak plate for minerals harder than 6.5. They scratch the streak plate. FIGURE 3.21 Mineral Database. This is an alphabetical list of minerals and their properties and uses. Mineral Properties, Identification, and Uses ■ 93 MINERAL DATABASE (Alphabetical Listing) Mineral CHALCOPYRITE CuFeS2 copper-iron sulfide Luster and Hardness Crystal System Metallic (M) 3.5–4 Distinctive Properties Streak Some Uses Dark gray Color bright silvery gold; Tarnishes bronze brown, brassy gold, or iridescent blue-green and red; Brittle; No cleavage; Forms dense masses or elongate tetrahedrons; SG = 4.1–4.3 Ore of copper, used to make pipes, electrical wire, coins, ammunition, bronze, brass; added to vitamin pills for healthy hair and skin Tetragonal CHERT SiO2 cryptocrystalline quartz Nonmetallic (NM) No visible crystals 7 White* Opaque gray or white; Luster waxy; Conchoidal fracture; SG = 2.5–2.8 Used as an abrasive; Used to make glass, gemstones CHLORITE ferromagnesian aluminum silicate Nonmetallic (NM) Monoclinic 2–2.5 White Color dark green; Cleavage excellent; Forms short prisms that split easily into thin flexible sheets; Luster bright or dull; SG = 2–3 Used as a “filler” (to take up space and reduce cost) in plastics for car parts, appliances; Massive pieces carved into art sculptures 5.5–6 Dark brown Color silvery black to black; Tarnishes gray to black; No cleavage; May be weakly attracted to a magnet; Forms dense masses or granular masses of small crystals (octahedrons) Ore of chromium for chrome, stainless steel, mirrors, yellow and green paint pigments and ceramic glazes, and pills for healthy metabolism and cholesterol levels Very light blue Color pale blue to blue-green; Opaque; Forms cryptocrystalline crusts or may be massive; Conchoidal fracture; Luster shiny or earthy; SG = 2.0–4.0 Ore of copper, used to make pipes, electrical wire, coins, ammunition, bronze, brass; added to vitamin pills for healthy hair and skin; Gemstone 2.5–3 Copper Color copper; Tarnishes brown or green; Malleable; No cleavage; Forms oddshaped masses, nuggets, or dendritic forms; SG = 8.8–9.0 Ore of copper, used to make pipes, electrical wire, coins, ammunition, bronze, brass; added to vitamin pills for healthy hair and skin 9 White* Gray, white, black, or colored (red, blue, brown, yellow) hexagonal prisms with flat striated ends; Opaque to transparent; Cleavage absent; SG = 3.9–4.1 H 9 Used for abrasive powders to polish lenses; gemstones (red ruby, blue sapphire); emery cloth 3.5–4 White Color white, gray, creme, or pink; Usually opaque; Cleavage excellent in 3 directions; Breaks into rhombohedrons; Resembles calcite, but will effervesce in dilute HCI only if powdered; SG = 2.8–2.9 Ore of magnesium used to make paper; lightweight frames for jet engines, rockets, cell phones, laptops; pills for good brain, muscle, and skeletal health 6–7 White* Color pale or dark green to yellow-green; Massive or forms striated prisms; Cleavage poor; SG = 3.3–3.5 Used as a green gemstone (Mg,Fe,Al)6(Si,Al)4O10(OH)8 Metallic CHROMITE (M) FeCr2O4 iron-chromium oxide Isometric CHRYSOCOLLA CuSiO3 · 2H2O hydrated copper silicate Nonmetallic (NM) COPPER (NATIVE COPPER) Cu copper Metallic (M) CORUNDUM Al2O3 aluminum oxide Nonmetallic (NM) 2–4 Orthorhombic Isometric Hexagonal DOLOMITE CaMg(CO3)2 magnesian calcium carbonate Nonmetallic (NM) Hexagonal EPIDOTE complex silicate Nonmetallic (NM) Monoclinic FELDSPAR: See PLAGIOCLASE (Na-Ca Feldspars) and POTASSIUM FELDSPAR (K-Spar) FLINT SiO2 cryptocrystalline quartz Nonmetallic (NM) No visible crystals 7 White* Color black to very dark gray; Opaque to translucent; Conchoidal fracture; Cryptocrystalline; SG = 2.5–2.8 Used as an abrasive; Used to make glass; Black gemstone FLUORITE CaF2 calcium fluoride Nonmetallic (NM) 4 White Colorless, purple, blue, gray, green, or yellow; Cleavage excellent; Crystals usually cubes; Transparent or opaque; Brittle; SG = 3.0–3.3 Ore of fluorine used in fluoride toothpaste, refrigerant gases, rocket fuel Isometric *Streak cannot be determined with a streak plate for minerals harder than 6.5. They scratch the streak plate. FIGURE 3.21 (continued) 94 ■ L A B O R AT O R Y 3 MINERAL DATABASE (Alphabetical Listing) Mineral GALENA PbS lead sulfide Luster and Hardness Crystal System Metallic (M) 2.5 Nonmetallic (NM) Color bright silvery gray; Tarnishes dull gray; Forms cubes and octahedrons; Brittle; Cleavage good in three directions, so breaks into cubes; SG = 7.4–7.6 Ore of lead for television glass, auto batteries, solder, ammunition; May be an ore of bismuth (an impurity) used as a lead substitute in pipe solder and fishing sinkers; May be an ore of silver (an impurity) used in jewelry, electrical circuit boards White* Color usually red, black, or brown, sometimes yellow, green, pink; Forms dodecahedrons; Cleavage absent but may have parting; Brittle; Translucent to opaque; SG = 3.5–4.3 Used as an abrasive; Red gemstone 5–5.5 Yellow-brown Color dark brown to black; Tarnishes yellow-brown; Forms layers of radiating microscopic crystals; SG = 3.3–4.3 Ore of iron for iron and steel used in machines, buildings, bridges, nails, tools, file cabinets; Added to pills and foods to aid hemoglobin production in red blood cells 2.5–3.0 Gold-yellow 7 Isometric GOETHITE Metallic FeO(OH) (M) iron oxide hydroxide Orthorhombic GOLD (NATIVE GOLD) Au pure gold Metallic (M) Isometric GRAPHITE C carbon Metallic (M) Nonmetallic (NM) HALITE NaCl sodium chloride Nonmetallic (NM) Color dark silvery gray to black; Forms flakes, short hexagonal prisms, and earthy masses; Greasy feel; Very soft; Cleavage excellent in 1 direction; SG = 2.0–2.3 Used for pencils, anodes (negative ends) of most batteries, synthetic motor oil, carbon steel, fishing rods, golf clubs 2 White Colorless, white, or gray; Forms tabular crystals, prisms, blades, or needles (satin spar variety); Transparent to translucent; Very soft; Cleavage good; SG = 2.3 Plaster-of-paris, wallboard, drywall, art sculpture medium (alabaster) 2.5 White Colorless, white, yellow, blue, brown, or red; Transparent to translucent; Brittle; Forms cubes; Cleavage excellent in 3 directions, so breaks into cubes; Salty taste; SG = 2.1–2.6 Table salt, road salt; Used in water softeners and as a preservative; Sodium ore 1–6 Red to red-brown Color silvery gray, reddish silver, black, or brick red; Tarnishes red; Opaque; Soft (earthy) and hard (metallic) varieties have same streak; Forms thin tabular crystals or massive; May be attracted to a magnet; SG = 4.9–5.3 Red ochre pigment in paint and cosmetics. Ore of iron for iron and steel used in machines, buildings, bridges, nails, tools, file cabinets; Added to pills and foods to aid hemoglobin production in red blood cells 5.5–6.0 White to pale gray Color dark gray to black; Forms prisms with good cleavage at 56° and 124°; Brittle; Splintery or asbestos forms; SG = 3.0–3.3 Fibrous varieties used for fire-resistant clothing, tiles, brake linings Monoclinic Metallic (M) or Nonmetallic (NM) Hexagonal HORNBLENDE Nonmetallic (amphibole) calcium (NM) ferromagnesian aluminum silicate Monoclinic Ductile and malleable metal used for jewelry; Electrical circuitry in computers, cell phones, car air bags; Heat shields for satellites Dark gray Isometric HEMATITE Fe2O3 iron oxide Color gold to yellow-gold; Does not tarnish; Ductile, malleable and sectile; Hackly fracture; SG = 19.3; No cleavage; Forms odd-shaped masses, nuggets, and dendritic forms 1 Hexagonal GYPSUM CaSO4 · 2H2O hydrated calcium sulfate Some Uses Gray to dark gray Isometric GARNET complex silicate Distinctive Properties Streak JASPER SiO2 cryptocrystalline quartz Nonmetallic (NM) No visible crystals 7 White* Color red-brown, or yellow; Opaque; Waxy luster; Conchoidal fracture; Cryptocrystalline; SG = 2.5–2.8 Used as an abrasive; Used to make glass, gemstones KAOLINITE Al4(Si4O10)(OH)8 aluminum silicate hydroxide Nonmetallic (NM) Triclinic 1–2 White Color white to very light brown; Commonly forms earthy, microcrystalline masses; Cleavage excellent but absent in hand samples; SG = 2.6 Used for pottery, clays, polishing compounds, pencil leads, paper 4–7 White* Color blue, pale green, white, or gray; Translucent to transparent; Forms blades; SG = 3.6–3.7 High temperature ceramics, spark plugs K-SPAR: See POTASSIUM FELDSPAR KYANITE Al2(SiO4)O aluminum silicate oxide Nonmetallic (NM) Triclinic *Streak cannot be determined with a streak plate for minerals harder than 6.5. They scratch the streak plate. Mineral Properties, Identification, and Uses ■ 95 MINERAL DATABASE (Alphabetical Listing) Mineral LIMONITE Fe2O3 · nH2O hydrated iron oxide and/or FeO(OH) · nH2O hydrated iron oxide hydroxide MAGNETITE Fe3O4 iron oxide Luster and Hardness Crystal System Metallic (M) or Nonmetallic (NM) Streak Distinctive Properties 1–5.5 Yellowbrown Color yellow-brown to dark brown; Tarnishes yellow to brown; Amorphous masses; Luster dull or earthy; Hard or soft; SG = 3.3–4.3 Yellow ochre pigment in paint and cosmetics. Ore of iron for iron and steel used in machines, buildings, bridges, nails, tools, file cabinets; Added to pills and foods to aid hemoglobin production in red blood cells 6–6.5 Dark gray Color silvery gray to black; Opaque; Forms octahedrons; Tarnishes gray; No cleavage; Attracted to a magnet and can be magnetized; SG = 5.0–5.2 Ore of iron for iron and steel used in machines, buildings, bridges, nails, tools, file cabinets; Added to pills and foods to aid hemoglobin production in red blood cells 3.5–4 Green Color green, pale green, or graygreen; Usually in crusts, laminated masses, or microcrystals; Effervesces in dilute HCl; SG = 3.6–4.0 Ore of copper, used to make pipes, electrical wire, coins, ammunition, bronze, brass; added to vitamin pills for healthy hair and skin; Gemstone 2–2.5 White Colorless, yellow, brown, or redbrown; Forms short opaque prisms; Cleavage excellent in 1 direction, can be split into thin flexible transparent sheets; SG = 2.7–3.0 Computer chip substrates, electrical insulation, roof shingles, Cosmetics with a satiny sheen 5–5.5 White Colorless, white, gray, or pale green, yellow, or red; Forms masses of radiating needles; Silky luster; SG = 2.2–2.4 Used in water softeners 7 White* Color pale or dark olive-green to yellow, or brown; Forms short crystals that may resemble sand grains; Conchoidal fracture; Cleavage absent; Brittle; SG = 3.3–3.4 Green gemstone (peridot); Ore of magnesium used to make paper; lightweight frames for jet engines, cell phones, laptops; pills for good brain, muscle, and skeletal health 5–5.5 White Colorless to white, orange, yellow, brown, blue, gray, green, or red; may have play of colors (opalescence); Amorphous; Cleavage absent; Conchoidal fracture; SG = 1.9–2.3 Gemstone 6 White Colorless, white, gray, or black; May have iridescent play of color from within; Translucent; Forms striated tabular crystals or blades; Cleavage good in two directions at nearly 90°; SG = 2.6–2.8 Used to make ceramics, glass, enamel, soap, false teeth, scouring powders 6 White Color orange, brown, white, green, or pink; Forms translucent prisms with subparallel exsolution lamellae; Cleavage excellent in two directions at nearly 90°; SG = 2.5–2.6 Used to make ceramics, glass, enamel, soap, false teeth, scouring powders 6–6.5 Dark gray Color silvery gold; Tarnishes brown; H 6–6.5; Cleavage absent to poor; Brittle; Forms opaque masses, cubes (often striated), or pyritohedrons; SG = 4.9–5.2 Ore of sulfur for matches, gunpowder, fertilizer, rubber hardening (car tires), fungicide, insecticide, paper pulp processing 3.5–4.5 Dark gray to black Color brassy to brown-bronze; Tarnishes dull brown, sometimes with faint iridescent colors; Fracture uneven to conchoidal; No cleavage; attracted to a magnet; SG = 4.6 Ore of iron and sulfur; Impure forms contain nickel and are used as nickel ore; the nickel is used to make stainless steel Amorphous Metallic (M) or Nonmetallic (NM) Isometric MALACHITE Cu2CO3(OH)2 copper carbonate hydroxide Nonmetallic (NM) Some Uses Monoclinic MICA: See BIOTITE and MUSCOVITE Nonmetallic MUSCOVITE MICA (NM) potassium hydrous aluminum silicate KAl2(Al,Si3O10)(OH,F)2 Monoclinic NATIVE COPPER: See COPPER NATIVE GOLD: See GOLD NATIVE SILVER: See SILVER NATIVE SULFUR: See SULFUR Nonmetallic NATROLITE (NM) (ZEOLITE) Na2(Al2Si3O10) · 2H2O hydrous sodium Orthorhombic aluminum silicate OLIVINE (Fe,Mg)2SiO4 ferromagnesian silicate Nonmetallic (NM) Orthorhombic OPAL SiO2 · nH2O hydrated silicon dioxide PLAGIOCLASE FELDSPAR NaAlSi3O8 to CaAl2Si2O8 calcium-sodium aluminum silicate Nonmetallic (NM) Amorphous Nonmetallic (NM) Triclinic Nonmetallic POTASSIUM (NM) FELDSPAR KAlSi3O8 potassium aluminum Monoclinic silicate PYRITE (“fool’s gold”) FeS2 iron sulfide Metallic (M) PYRRHOTITE Metallic (M) FeS iron sulfide Isometric Monoclinic *Streak cannot be determined with a streak plate for minerals harder than 6.5. They scratch the streak plate. 96 ■ L A B O R AT O R Y 3 MINERAL DATABASE (Alphabetical Listing) Mineral Luster and Crystal Hardness System Distinctive Properties Streak Some Uses PYROXENE: See AUGITE QUARTZ SiO2 silicon dioxide Nonmetallic (NM) 7 White* Hexagonal Usually colorless, white, or gray but uncommon varieties occur in all colors; Transparent to translucent; Luster greasy; No cleavage; Forms hexagonal prism and pyramids; SG = 2.6–2.7 Used as an abrasive; Used to make glass, gemstones Some quartz varieties are: • var. flint (opaque black or dark gray) • var. smoky (transparent gray) • var. citrine (transparent yellow-brown) • var. amethyst (purple) • var. chert (opaque gray) • var. milky (white) • var. jasper (opaque red or yellow) • var. rock crystal (colorless) • var. rose (pink) • var. chalcedony (translucent, waxy luster) SERPENTINE Mg6Si4O10(OH)8 magnesium silicate hydroxide Nonmetallic (NM) SILLIMANITE Al2(SiO4)O aluminum silicate Nonmetallic (NM) 2–5 White Color pale or dark green, yellow, gray; Forms dull or silky masses and asbestos forms; No cleavage; SG = 2.2–2.6 Fibrous varieties used for fire-resistant clothing, tiles, brake linings 6–7 White Color pale brown, white, or gray; One good cleavage plus fracture surfaces; Forms slender prisms and needles; SG = 3.2 High-temperature ceramics 2.5–3.0 White to silvery white Color silvery white to gray; Tarnishes dark gray to black; Ductile, malleable and sectile; Hackly fracture; No cleavage; Forms nuggets, curled wires, and dendritic forms; SG = 10.5 Ductile and malleable metal used for jewelry and silverware; Electrical circuit boards for computers and cell phones; Photographic film 3.5–4 White to pale yellow-brown Color silvery yellow-brown, dark red, or black; Tarnishes brown or black; Dodecahedral cleavage excellent to good; Smells like rotten eggs when scratched/powdered; Forms misshapen tetrahedrons or dodecahedrons; SG = 3.9–4.1 Ore of zinc for brass, galvanized steel and roofing nails, skin-healing creams, pills for healthy immune system and protein production: Ore of Indium (an impurity) used to make solar cells 7 White to gray* Color brown to gray-brown; Tarnishes dull brown; Forms prisms that interpenetrate to form natural crosses; Cleavage poor; SG = 3.7–3.8 Gemstone crosses called “fairy crosses” Pale yellow Color bright yellow; Forms transparent to translucent crystals or earthy masses; Cleavage poor; Luster greasy to earthy; Brittle; SG = 2.1 Used for matches, gunpowder, fertilizer, rubber hardening (car tires), fungicide, insecticide, paper pulp processing 1 White Color white, gray, pale green, or brown; Forms cryptocrystalline masses that show no cleavage; Luster silky to greasy; Feels greasy or soapy (talcum powder); Very soft; SG = 2.7–2.8 Used as a “filler” (to take up space and reduce cost) in plastics for car parts, appliances; Massive pieces carved into art sculptures 7–7.5 White* Color usually opaque black or green, but may be transparent or translucent green, red, yellow, pink or blue; Forms long striated prisms with triangular cross sections; Cleavage absent; SG = 3.0–3.2 Crystals used in radio transmitters; gemstone Monoclinic Orthorhombic SILVER (NATIVE SILVER) Ag pure silver Metallic (M) SPHALERITE ZnS zinc sulfide Metallic (M) or Nonmetallic (NM) Isometric Isometric STAUROLITE iron magnesium zinc aluminum silicate Nonmetallic (NM) SULFUR (NATIVE SULFUR) S sulfur Nonmetallic (NM) TALC Mg3Si4O10(OH)2 hydrous magnesian silicate Monoclinic 1.5–2.5 Orthorhombic Nonmetallic (NM) Monoclinic TOURMALINE complex silicate Nonmetallic (NM) Hexagonal ZEOLITE: A group of calcium or sodium hydrous aluminum silicates. See NATROLITE. *Streak cannot be determined with a streak plate for minerals harder than 6.5. They scratch the streak plate. Mineral Properties, Identification, and Uses ■ 97 2012 U.S. NET IMPORT RELIANCE ON SELECTED NON-FUEL MINERAL COMMODITIES COMMODITY (Element, Ore, or Raw Mineral) ORE MINERAL or RAW MINERAL Percent Import Reliance Fluorine ore (F): fluorspar Fluorite 100 Graphite (C) Graphite 100 Indium metal (In) 100 Mica (sheet) Sphalerite with In as an impurity Muscovite Quartz crystal (industrial) Niobium metal (Nb, “columbium”) Quartz var. rock crystal Columbite (in “coltan”) 100 Tantalum metal (Ta) Tantalite (in “coltan”) 100 Gallium metal (Ga) Bauxite is Ga ore 99 Vanadium metal (V) Magnetite with V as an impurity 96 Bismuth metal (Bi) Galena with Bi as an impurity 92 Bismuth is used as a nontoxic replacement for lead (in ceramic glazes, fishing sinkers, food processing equipment, plumbing, and shot for hunting) and in antidiarrheal medications. Barium metal ore (Ba) Zinc metal (Zn) Barite 80 Sphalerite is an ore of Zn 72 Barium (Ba) is widely used to make capacitors (that store energy) and memory cells in cell phones and other portable electronic devices. Zinc is used to make alloys like brass, skin-healing creams, and galvanized (rust-proof) steel and roofing nails; added to vitamin pills for a healthy immune system and to aid protein production. Chromium metal (Cr) Chromite is an ore of Cr 70 Chromium is used to make stainless steel, yellow and green ceramic glazes and paints, and military camouflage paints; added to vitamin pills for healthy metabolism and lower cholesterol levels. Garnet (industrial) Garnet 65 Silver metal (Ag) Native silver; Galena with Ag as an impurity Pyrrhotite contains Ni as an impurity 57 Industrial garnet is used as an abrasive in things like sandpaper and sandblasting. Silver is used to make jewelry and silverware, photographic film, and solder on electrical circuit boards of computers and cell phones. 49 Nickel is used to make rechargeable batteries (Ni-Cd) for portable electronic devices, screw-end caps of light bulbs, and stainless steel. Magnesium metal (Mg) Dolomite and Olivine are Mg ores 46 Magnesium is used to make strong, lightweight frames for jet engines and rockets, lightweight cell phone and laptop cases, and incendiary flares and bombs; added to vitamin pills to aid good brain and muscle function and strengthen bones. Tungsten metal (W) Wolframite is W ore 42 Tungsten is a dense metal that makes cell phones and pagers vibrate (by attaching it to an electric motor spinning off center); also used for light bulb filaments, golf clubs, and tungsten carbide cutting tools. Copper metal (Cu) 35 Aluminum (Al) Azurite, Bornite, Chalcopyrite, Chrysocolla, and Malachite are Cu ores Bauxite is Al ore Salt Halite 19 Sulfur (S) Native Sulfur; Pyrite is a S ore 19 Copper is used to make copper pipes; electrical wire for homes, businesses, electric motors, and circuit boards in cell phones and other electrical devices. Hybrid cars contain about 100 pounds (45 kg) of copper. Added to vitamin pills for healthy hair and skin. Aluminum is a lightweight silvery metal used to make drink cans, foil, airplanes, and solar panels. Used as table salt, road salt (to melt snow), in water softeners, and as a food preservative. Used to make matches, gunpowder, fertilizer, fungicide, insecticide, and harden rubber (car tires). Nickel metal (Ni) 100 100 20 WHAT IS THIS COMMODITY USED FOR? Fluorine is used in fluoride toothpaste, fluorocarbon refrigerant gases and fire extinguishers, and fluoropolymer plastics that coat non-stick fry pans and insulate wiring in cell phones, laptops, and airplanes. Used to make carbon steel, pencils, carbon fiber reinforced plastics in car bodies, and negative ends of most batteries (including those in all cell phones, power tools, computers, and hybrid/electric vehicles). Indium is used to make solar cells, and liquid-crystal displays (LCDs) in cell phones, computers, and flat-screen television sets. Muscovite is used in heating elements of hair dryers and toasters, joint compound, and cosmetics with a satiny or glittery sheen. Crystals of cultured pure quartz are used to make quartz watches and the frequency controls and timers in every computer and cell phone. Niobium is used to make high-strength non-corrosive steel alloys (for jet engines, power plants) and arc welding rods, plus electrical insulation coatings in cell phones, computers, and electronic games. Tantalum is used to make “tantalum capacitors” that buffer the flow of electricity between a battery and electronic parts in the circuits of cell phones, laptops, iPods, and most other electrical devices. Gallium is used to make light-emitting diode (LED) bulbs and liquid-crystal displays (LCDs) in things like cell phones, computers, and flat-screen television sets. Vanadium is used for cutting tools; mixed with iron to make lightweight shock-resistant steel for car axles and gears, springs, and cutting tools. Gypsum Gypsum 12 Used to make Plaster-of-Paris, drywall and for art (alabaster). Iron metal (Fe), Steel Geothite, Limonite, Magnetite, and Hematite are Fe ores 11 Iron and steel a..

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