The categorization of sedimentary rocks according to the way they formed, as either clastic or chemical. Clastic rocks consist of fragments of weathered (see weathering) rock cemented together (see cementation). Chemical sedimentary rocks form when minerals dissolve in water and are later deposited as solids. The tables show a selection of both categories.
Clastic Sedimentary Rocks
Rock | Type of sediment | Texture |
|---|
Conglomerate | Gravel with rounded fragments | Coarse (>2 mm) |
Breccia | Gravel with angular fragments | Coarse (>2 mm) |
Sandstone | Sand | Medium (0.06–2 mm) |
Siltstone | Mud | Fine (4–62.75 µm) |
Shale | Mud | Very fine (<4 µm) |
Chemical Sedimentary Rocks
Rock | Composition | Texture |
|---|
Crystalline limestone | Calcite (CaCO3) | Coarse to fine crystalline |
Fossiliferous limestone | Calcite (CaCO3) | Visible shell fragments |
Chalk | Calcite (CaCO3) | Microscopic shells and clay |
Chert | Quartz (SiO2) | Very fine crystalline |
Gypsum | Gypsum (CaSO4.2H2O) | Fine to coarse crystalline |
Rock salt | Halite (NaCl) | Fine to coarse crystalline |
Bituminous coal | Organic matter | Fine |