Sedimentary rock is classified into two main categories: clastic and chemical. Clastic or detrital sedimentary rocks are made from pieces of bedrock, sediment, derived primarily by mechanical weathering. Clastic rocks may also include chemically weathered sediment.
How Do Geologists Classify Sedimentary Rock?
Geologists classify sedimentary rocks according to their origin, composition and texture. The most common types of sedimentary rocks include sandstone, shale, limestone, and conglomerate. Each type has its own characteristics that help geologists identify and classify it.
The origin of sedimentary rocks is the key factor in their classification. Sedimentary rocks can form from organic material, such as shells and bones, from chemical reactions, from the erosion of other rocks, or from the evaporation of a liquid. Depending on the origin, sedimentary rocks are divided into four main categories: clastic, chemical, biochemical, and organic.
Clastic sedimentary rocks are formed from the accumulation of weathered rock fragments. These fragments can be anything from small pieces of clay to large boulders. Geologists can classify these rocks according to the size of the fragments, or the lithology of the fragments. Common clastic rocks include sandstone and conglomerate.
Chemical sedimentary rocks are formed when minerals are dissolved in water and then redeposited in layers. These rocks contain minerals such as calcite, gypsum, and halite. Common chemical rocks include limestone and dolostone.
Biochemical sedimentary rocks are formed from the