Q. Which of the following is/are correctly matched?
Mechanism/Process: Rock
1. Mechanically formed sedimentary rock:Sandstone
2. Organically formed sedimentary rock:Dolomites
3. Chemically formed sedimentary rock:Shale
Select the correct answer using the code given below:

[A] 1 only

[B] 1 and 2 only

[C] 2 and 3 only

[D] 1, 2 and 3

Answer: B

Sedimentary rocks are formed by the accumulation of sediments. There are three basic types of sedimentary rocks. 

  • Clastic sedimentary rocks such as breccia, conglomerate, sandstone, siltstone, and shale are formed from mechanical weathering debris. 
  • Chemical sedimentary rocks, such as rock salt, iron ore, chert, flint, some dolomites, and some limestone, form when dissolved materials precipitate from solution. 
  • Organic sedimentary rocks such as coal, some dolomites, and some limestone, form from the accumulation of plant or animal debris. 

Source: G C Leong