Sedimentary rocks are also known as secondary rocks as they are formed from the sediments of other rocks denuded and deposited by the agents of gradation. Classification of sedimentary rocks on the basis of various factors:
Classification of Sedimentary Rocks
Classification of Sedimentary Rocks On the basis of processes
Evaporation: When the water evaporates, it leaves behind deposits of one or more chemicals. These chemicals are compacted and cemented to form rocks.
Compaction: When soft and loose sediments are squeezed by overlying layers of rocks and rocks lying beneath them, they become hardened. For example, sandstone is formed after compacting of sand.
Cementation: Binding together compacted sediments by natural materials such as silica and iron is called cementation.
Classification of Sedimentary Rocks On the basis of the formation
Mechanically formed rocks: When old rocks are denuded and broken into fragments by running water or moving glaciers, they are deposited on new lands resulting in the formation of rocks.
Chemically formed rocks: They are formed when chemical sedimentation takes place generally because of the evaporation of water-containing salts in the solution.
Organically formed rocks: These rocks are formed when the remains of plants and animals get compressed forming a rock. For example, limestone and lignite.
Classification of Sedimentary Rocks On the basis of agents of formation
Riverine rocks: These rocks are formed by the deposition of alluvial soil by streams of water.
Lacustrine rocks: These are found on the bed of a lake after long periods of deposition.
Glacial rocks: These are formed because of the deposition of debris by glaciers.
Aeolian rocks: The cementation of sand particles brought by winds result in the formation of Aeolian rocks.
Marine rocks: These rocks are formed on the ocean floor. There are two types of marine rocks. Calcareous marine rocks are formed by the deposition of shells and skeletons of sea organisms.
Carbonaceous rocks: These rocks are formed when sea plants and animals are buried under the sea for a long period of time.