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LEQ: What characteristics are used to classify and identify sedimentary rock?
Key Terms: clast, clastic rock, biochemical/organic rock, chemical rock
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Classifying Sedimentary Rock Review
Geologists classify sedimentary rock according to the type of sediment that make up the rock. Clastic Sedimentary Rock Sediment type: Rock fragments Organic (Biochemical) Sedimentary Rock Sediment type: Organic material Chemical Sedimentary Rock Sediment type: dissolved mineral crystallization.
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Clastic Sedimentary Rock
Most sedimentary rocks are in this group. Form when rock fragments (clasts) are compacted and cemented together. Clasts vary in size. Clastic sedimentary rocks are grouped by the size of the clasts that make up the rock. Clasts (rock fragments) in a clastic sedimentary rock are also observe for their Grain shape How well the grains are sorted.
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Sediment Grain Size Scale
Gravel Sand Silt Clay
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Clastic Sedimentary Rock Sediment Size Chart (The Wentworth Scale)
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Grain Shape Grain shape is observed as angular or rounded, and is described as indicated in the examples below.
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Grain Sorting How well sorted the clasts are sorted is also observed as indicated in the examples below.
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Common Clastic Sedimentary Rocks Sediment Size: Gravel
Conglomerate: rounded grain well sorted Breccia: angular grain poorly sorted
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Common Clastic Sedimentary Rocks Sediment Size: Sand
Sandstone
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Common Clastic Sedimentary Rocks Sediment Size: Silt, Clay, Mud
Shale or Mudstone
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Organic Sedimentary Rock
Also known as biological or biochemical sedimentary rocks. Form when organic material (remains of plants or animals) are compacted and cemented together. Organic sedimentary rocks are identified by the type of organic material that makes up the rock.
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Organic Sedimentary Rocks: Sediment: Plant Remains
Coal Peat Both contain an abundance of Carbon
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Organic Sedimentary Rocks: Sediment: Animal Remains
Limestone Chalk Both contain an abundance of Calcium Carbonate Calcium Carbonate reacts with Hydrochloric Acid (fizz test)
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Chemical Sedimentary Rock
Also known as evaporites. Form from the crystallization of dissolved minerals in a solution. The liquid (water) evaporates Dissolved minerals crystallize as the water evaporates. Identified by the mineral that crystallizes.
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Chemical Sedimentary Rocks
Rock Salt Rock Gypsum Crystallized Limestone
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