Sedimentary rocks are formed from sediments accumulated over long periods, usually under water on the floors of shallow seas, rivers and lakes. These rocks are non-crystalline and are found in layers or strata and contain fossils. Conglomerate, sandstone, limestone, chalk, calcite, and dolomite are example of sedimentary rocks. 

Sedimentary rocks are divided into various types depending on how they are formed. 

1. Mechanically formed sedimentary rocks : These rocks have been formed by the accumulation of materials derived from other rocks which have been cemented together. Examples – conglomerate (rounded fragments), breccia (angular fragments). 

2. Organically formed sedimentary rocks : These rocks have been formed by the accumulation of the remains of living organisms. Examples – calcareous rocks such as limestone and chalk. 

3. Chemically formed sedimentary rocks: These rocks have been commonly formed by the process of evaporation of water containing salts in solution. 

Examples – rock salt, gypsum, potash, nitrates, calcite, and dolomite.