Rock classification by dominant composition If a rock is dominated by calcium carbonate (CaCO3), how is it classified?

Introduction / Context:Classifying rocks by dominant chemical composition aids in predicting durability, reactivity, and suitability for construction. Calcium carbonate–rich rocks behave differently from silica- or clay-rich varieties.

Given Data / Assumptions:

• The rock is predominantly calcium carbonate (e.g., limestone, marble).
• Intended use may include masonry, aggregates, or decorative stone.

Concept / Approach:Rocks are often grouped as siliceous (quartz-rich), argillaceous (clay-rich), or calcareous (calcium carbonate–rich). Calcareous stones effervesce with dilute acid and can be sensitive to acidic environments, impacting selection and maintenance.

Step-by-Step Solution:

Verification / Alternative check:Simple acid tests (dilute HCl) confirm carbonate presence by visible effervescence.

Why Other Options Are Wrong:

• Siliceous (A): silica-rich (sandstone, granite) rather than carbonate.
• Argillaceous (B): clay-rich (shales, slates).
• None of these (D): incorrect because “calcareous” is the accepted term.

Common Pitfalls:Confusing marble (metamorphosed limestone) with siliceous stones; composition, not origin, dictates this classification.

Final Answer: