The instructor will advise you if a sample has a particular taste. 3 Smell- some minerals have unique smells, such as sulfur (S) which smells like rotten eggs. The minerals Galena and Pyrite (Fools Gold), which are sulfide minerals, contain a metal plus sulfur atoms. Smell is a special property. Density (D=M/V) – is the amount of material per unit volume (g/ml). Some minerals, like gold or galena, have a high density (g/ml) and are very “heavy” since they contain “heavy” atoms such as lead. Density is a property highly influenced by chemical composition. Density is calculated by measuring the mass of a sample and dividing it by its volume (the space it occupies). To find the density of a mineral sample you do the following: 1) Measure the dry specimen on a scale and obtain the mass in grams (g). 2) Take a large-mouthed plastic graduated cylinder and add 150 milliliters (ml) water to it. Gently slide the mineral sample into the water and let it sink. Holding the cylinder upright, measure the new water mark. Check graduation scale since some lines represent 5 ml and others the volume between each line may represent 10 ml. Take this number and subtract it from 150 to get the number of milliliters or the volume of the sample. 3) To get the density (D), divide the number of grams (g) by the numbers of ml (ml). A sample problem is done for you below: Sample (unknown) Number: M99 Mass: 200 g Starting water volume: 150 ml Ending water volume: 160 ml Volume of the sample: 160 – 150 = 10 ml Density: 200 g/ 10 ml = 20 g/ml 4 Specific Gravity (s.g.) is the ratio of the density of a mineral compared to the density of an equal volume of water. Since the average density of water is 1g/ml, the specific gravity is usually the same value/number as the density with no units. Ex: The density of gold is approximately 20 g/ml. The density of water is about 1 g/ml. The specific gravity of gold is: s.g. = Dgold/Dwater = 20g/ml / 1g/ml = 20 Since gold has a specific density of 20 we would say that given equal volumes of gold and water, gold is approximately 20 x denser than water. Tenacity- some minerals, like the mica sheets, can be bent without breaking and return to their original shape. This is considered a special property. Malleability- some of the minerals, primarily the metallic minerals, can be shaped, flattened or hammered. Copper is a malleable mineral. This is a special property. Magnetism- some minerals contain large quantities of iron atoms which promote magnetism. Magnetism is a special property. Hardness- is the ability of a mineral to resist scratching. Because of their unique atomic composition and alignment, some minerals will scratch others (Mohs Scale). Talc is the softest mineral (rating = 1) and is scratched by all other known minerals. Diamond is the hardest mineral (rating = 10) and scratches all other known minerals. You can compare the hardness of your sample to various other materials such as glass (5.5), copper (3.5) and even the human fingernail (2.5). 5 Hardness is reported/recorded using the following scales: Mineral does not scratch your finger nail………………… (< 2.5) Hardness less than 2.5 Mineral scratches fingernail but not copper strip………… (2.5 – 3.5) between 2.5 and 3.5 Mineral scratches copper strip but not glass plate………… (3.5 – 5.5) between 3.5 and 5.5 Mineral scratches the glass plate………………………… 5.5) greater than 5.5 (> If the sample and the known material DO NOT SCRATCH each other this means that both items have the same hardness! A sample of the mineral quartz scratches a glass plate. 6 Cleavage/fracture- because of their crystalline structure, some minerals will break and produce smooth lines (cleavage) while others will produce irregular planes (fracture). Regardless of size, samples of the same mineral that exhibits cleavage will always have the same cleavage, thus the same angles. The following terms are used to describe cleavage: 0 directions of cleavage (fracture) 1 direction of cleavage (sheet) 2 directions at 900 (rectangle) 2 directions not at 900 (parallelogram) 3 directions at 900 (cube) 3 directions not at 900 (rhombohedron) 4 directions (octahedron) 7 Streak- because of their internal atomic makeup, some minerals leave distinctlycolored streaks when rubbed against a WHITE porcelain plate. Note the color of the streak if present. If the streak is lighter in color, use the black streak plate. Some samples may not produce a streak at all depending on the sample’s hardness. 8 The mineral graphite, exhibiting metallic luster and a dark streak, is shown above. Luster- minerals may also have metallic (metal-like), glassy or pearly exteriors while other minerals may not have a metallic luster at all (dull, earthy). Terms used: metallic (shines like a metal), non-metallic (does not shine like a metal) and additional terms used to describe non-metallic minerals include: earthy, dull, soil-like, concrete, pearly and glassy. The two varieties of the mineral hematite are shown (metallic and dull) above. 9 Acid test- some minerals, primarily those that are made up of carbonate or CO3 like calcite, will fizz or effervesce when in contact with a few drops of hydrochloric acid. The carbonate has been converted into carbon dioxide (CO2) which causes the bubbles. Goggles and gloves are to be worn when performing the acid (chemical) test. Terms used: Acid negative (-) or acid positive (+) (fizzes = special property) A sample of the mineral calcite is shown above reacting positively to acid. Crystal form or habit- represents the external appearance or shape of a mineral that results from an orderly internal arrangement of atoms under natural, un-restricted conditions. This is NOT the same as cleavage! This property is influenced by crystalline structure. Most samples, such as quartz, have a crystalline structure BUT due to overcrowding and pressure do not exhibit these forms readily. 10 11 CLASSIFICATION OF MINERALS: There are two basic types or classes of the 4000+ minerals: the silicates and non-silicates. 1) SILICATES- THESE MINERALS CONTAIN THE SILICON-OXYGEN (SiO4) TETRAHEDRAL and make up the majority of mineral located in the Earth’s crust. 2) NON-SILICATES – THESE MINERALS DO NOT CONTAIN THE SILICONOXYGEN TETRAHEDRAL AND ARE FURTHER SUBDIVIDED INTO THE FOLLOWING CATEGORIES: • • • • • • NATIVES – Silver (Ag), gold (Au), platinum (Pt), and carbon (C). CARBONATES- these minerals have carbonate (CO3) and will respond (fizz) when in contact with acid. HALIDES- these minerals will have either chlorine (Cl) or Fluorine (F) SULFIDES- these minerals contain Sulfur (S) and an additional type of atom SULFATES- these minerals contain Sulfur (S) and oxygen (O) which form sulfate (SO4) OXIDES- these minerals contain oxygen (O). COMMON MINERAL USES: 1) SILVER (Ag) – photography,

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