Question

Consider the following regarding rock examples:

1. Fossiliferous limestone is a type of biochemical rock
2. Shale is a fragment-based mechanical rock.
3. Rock salt is formed from organic remains.

• A. All
• B. ii only
• C. i, iii
• D. i, ii

Answer 1

Answer:

D. i, ii

Types of Rocks and Their Formation

Biochemical Rocks:

• Fossiliferous limestone is a prime example of a biochemical sedimentary rock.
• It is formed when marine organisms, such as corals, mollusks, and foraminifera, secrete calcium carbonate to build their shells and skeletons.
• Upon their death, these hard parts accumulate on the seafloor and eventually lithify (turn into rock) to form limestone.
• The presence of fossils is a direct indicator of its biological origin.

Mechanical (Clastic) Sedimentary Rocks:

• Shale is classified as a fragmental or clastic sedimentary rock.
• It is composed primarily of clay minerals and fine-grained silt particles that have been transported by wind or water.
• These fine particles settle in low-energy environments, such as deep ocean basins or lake beds, and are compacted and cemented together.
• The term 'fragment-based' accurately describes its formation from accumulated fragments of other rocks and minerals.

Evaporite Rocks:

• Rock salt (halite) is a chemical sedimentary rock, specifically an evaporite.
• It forms when bodies of water, such as saltwater lakes or restricted marine basins, evaporate, leaving behind dissolved mineral salts.
• The primary mineral in rock salt is halite (NaCl).
• Its formation is a process of precipitation from a solution due to evaporation, not from organic remains.