Engineering geology — classification of limestone by origin Limestone (chiefly calcium carbonate) belongs to which category and is not which of the following?

Introduction / Context:
Limestone is a common construction material used for aggregates, cement manufacture, and dimension stone. Correctly recognizing its geological class supports decisions about durability, weathering, and suitability for lime production.

Given Data / Assumptions:

• Limestone forms predominantly by precipitation/biochemical processes in marine or lacustrine environments.
• It shows stratification typical of sedimentary deposition.
• Metamorphic transformation of limestone yields marble, a different rock.

Concept / Approach:
Rocks are broadly categorized as igneous, sedimentary, or metamorphic. Limestone is sedimentary and typically stratified (layered). It is also an aqueous rock in origin because water-based chemical/biochemical processes produce it. Therefore, the class limestone is not is “metamorphic rock.”

Step-by-Step Solution:
Identify origin: chemical/biochemical precipitation of CaCO3 → sedimentary.Note structure: bedding/stratification common in limestone sequences.Aqueous association: deposition in water-driven environments.Exclude metamorphic category: metamorphism would convert limestone to marble.

Verification / Alternative check:
Field evidence: fossils, bedding planes, and sedimentary structures in limestone sequences confirm its sedimentary nature.

Why Other Options Are Wrong:
Options (a), (b), and (c) correctly describe limestone; selecting them would contradict well-established geology.

Common Pitfalls:
Confusing marble (metamorphosed limestone) with unaltered limestone; misreading “aqueous” as “aquifer,” which is unrelated to genesis classification.

Final Answer:
Metamorphic rock