EXERCISES Sedimentary Rocks Exercises PRE-LAB EXERCISES Answer these questions before looking at the sedimentary rock specimens to be sure that you have mastered the material in the lab. 1. Which of the following are terrigenous sedimentary rocks? Draw a circle around them. Black shale Arkose Intraclastic limestone Diatomite Rock gypsum Quartz conglomerate Oolitic limestone Red sandstone Lignite Graywacke Chert Bituminous coal 2. There are three white, fine-grained sedimentary rocks. What distinguishing characteristics might you use to tell them apart? Chalk Kaolin Diatomite 3. What is the main difference between shale and claystone? 4. For each of the rock types in the table below, give the name of the dominant mineral, the chemical formula of that mineral, and tell whether or not the mineral (or rock) will effervesce (fizz) in hydrochloric acid. Rock Type Mineral Name Chemical Formula Reaction to HCI Limestone Dolostone Rock gypsum Rock salt Chert Travertine Sedimentary Rocks Exercises 107 Sedimentary Rocks 109 . Instructions for Filling in the Sedimentary Rock Identification Table Column 1: Grain Size (If Visible) There are three ways to measure grain size: Measure the size of the grains in millimeters with a ruler. This works well for gravel-sized clasts, but it may be difficult for finer-grained samples. Compare the grain size to that of reference sediment textures on a grain-size comparator or sand gauge. This works well for distinguishing sandstone from siltstone. List whether the sample consists of gravel, sand, silt, or clay particles based on a simple visual inspection. If you cannot see grains, write “Grains not visible.” . Column 2: Minerals or Grain Type Identify the minerals present (calcite, dolomite, gypsum, halite, quartz, feldspar, clay minerals, etc.) If grains (clasts or allochems) are present, what are they? (Possibilities include fossils, oolites, intraclasts, and mineral grains or rock fragments.) . Column 3: Fizz in HCI? . Use dilute hydrochloric acid to test the sample to determine whether calcium carbonate (calcite or aragonite) or dolomite is present. Calcite and aragonite readily fizz in acid. Dolomite fizzes only if scratched or powdered. If it fizzes readily, write “Yes.” If it fizzes only when scratched and powdered, write “Only if powdered.” If it does not fizz, write “No.” . Column 4: Describe . Use this column to describe the sample. For example, the color, any layers, or any other distinguishing features. Column 5: Sedimentary Rock Name Identify the rock. Use Table 4.3 and Table 4.4 in the section Classification of Sedimentary Rocks. If you are in the lab, and if there are examples of “known” samples, you may also use them for comparison. Grain Size (if visible) Minerals or Grain Type Fizz in HCI? Describe Sedimentary Rock Name 1 2 3 4 5 108 Sedimentary Rocks 5. Classify the following terrigenous rocks according to whether they are: (a) rudites, (b) arenites, or (c) argillites. Put the letter in the blank. Lithic sandstone Conglomerate with quartz clasts Arkose Gray silty shale Breccia with iron oxide cement Kaolinite 6. Classify the following carbonate rocks according to whether they are (a) calcirudites, (b) calcarenites, or (c) calcilutites. Put the letter in the blank. Intraclastic limestone Chalk Oolitic limestone Coquina Micrite 7. Match the rock type with the sediment from which it is formed. Put the letter in the blank. micrite shale graywacke a. rounded gravel b. plant fragments c. microscopic skeletons of silica d. feldspar grains e. angular gravel f. sand-sized rock fragments chalk diatomite lignite g. clay coquina arkose h. lime mud i. broken shells conglomerate breccia j. coccoliths 8. List three allochems you might find in limestone. LAB EXERCISES Sedimentary Rock Identification Instructions Examine the sedimentary rock samples provided by your instructor. Fill in the chart below, and use Table 4.3 and Table 4.4 in the section Classification of Sedimentary Rocks to help you identify the samples. 110 Sedimentary Rocks Grain Size (if visible) Minerals or Grain Type Fizz in HCI? Describe Sedimentary Rock Name 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Sedimentary Rocks 111 OPTIONAL ACTIVITY 1. Examine samples of sand using a hand lens or a microscope, and answer the following questions. (Some questions might have more than one answer.) a. Which sand is better sorted? b. Which sand contains skeletons of microscopic marine animals? c. Which sample contains sand grains derived from rock weathering? d. Which sample might have been collected from a river? e. Which sample might have been collected from a warm, shallow sea? 2. Using a microscope, examine the thin sections provided by your instructor. Put the number of the thin section in the correct blank. a. Оolitic limestone b. Fossiliferous limestone c. Quartz sandstone d. Arkose e. Shale f. Siltstone g. Lithic sandstone (graywacke) h. Pelleted limestone i. Micrite or chalk j. Dolostone
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