Question

How are sedimentary rocks classified?

Answer 1

Sedimentary rocks are classified into the following types according to the nature of sediments, their origin, composition and the mode of formation.

1. Inorganic rocks or Mechanically-formed Sedimentary Rocks :- These type of rocks are formed by the deposition of land derived material. When the river began to flow, they eroded the rocks and washed away to the sea. Clay, shale, sandstone were formed in this way. These rocks are called inorganic rocks.
2. Organically formed Sedimentary Rocks :- These rocks are formed by the deposition of plants and sea organisms. Millions of years ago, there grew huge forest in marshy places. In course of ages they were buried underground and the internal heat changed them into coal. Moreover, there are millions and millions of sea-organisms whose skeleton are made of Calcium carbonate derived from sea water. After their death skeleton sink to the bottom of the seas and are formed into lime true and chalk and coal.
3. Chemically-formed Sedimentary Rocks :- There rocks are formed by the evaporation of water from solution containing mineral. Various kinds of salts precipitate from waters of shallow desert lakes, where evaporation of the water is rapid. Gypsum is the best example of this kind of rocks. Several nitrates and potash are also chemically formed sedimentary rocks.