Sedimentary rocks are formed at the Earth’s surface by the accumulation and cementation of fragments of earlier rocks, minerals and organisms or as chemical precipitates and organic growth in water (sedimentation).
Sediments are formed by weathering of earlier rocks (Igneous, sedimentary and metamorphic) by erosion from a source and are then transported to the place of deposition by water, wind, ice, mass movement of glaciers (agents of denudation).
After this through the process of Lithification, loose, unconsolidated sediments are turned into solid sedimentary rocks.
Many sedimentary rocks are able to retain their specific characteristics in their depository layer, even after lithification. It is the reason why sand stones have multiple layers of different concentrations.
Sedimentary rocks are formed by the accumulation of sediments. There are three basic types of sedimentary rocks-
(i) Sedimentary Rocks formed as a result of Mechanical processes- Ex - Limestone, sand- stones, shale, Conglomerate etc.
(ii) Carbonic sedimentary Rocks - geyserite, lime stone, coal, etc.
(iii) Chemical sedimentary rocks - Limestone, healite, potassium, etc.
