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Sedimentary Rock Identification

Sedimentary Rock Identification

Rock - Sedimentary - SandstoneIntroduction: The next time you get the chance, look around outside for a rock. Most likely, you will find a sedimentary rock. Although igneous and metamorphic rocks are far more common, sedimentary rocks are found mainly on the thin outer covering of the crust where weathering occurs. Understanding how to identify a sedimentary rock tells us more than just its name. It helps us piece together the story of how and where the rock formed.

Geologists classify sedimentary rocks based mainly on how they form. Clastic sedimentary rocks form from the compaction and cementation of sediments. These rocks tend to look and feel "grainy." Look at the size of the grains to help determine the name of a clastic rock. Chemical sedimentary rocks form from dissolved minerals that precipitate from water or remain behind after water evaporates. These rocks are made of crystallized minerals and tend to look more consolidated than clastic rocks. Try to determine the dominant mineral that makes up the rock to figure out the name of a chemical rock. Organic sedimentary rocks are made from the remains of plant or animal materials. Some classification schemes combine chemical and organic rocks into a single category.

Using a sedimentary rock chart like the one shown can help with the process of rock identification.
Chart - Sedimentary Rocks

 

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