Limestone

Physical Properties

Hardness: 3 on Mohs scale; Color: light gray to tan; Luster: dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: Rhombohedral (rarely visible in fine-grained specimens); Specific Gravity: 2.5-2.7

Formation & Geological History

Formed primarily in shallow marine environments from the accumulation of coral, shell, and algal debris over millions of years (primarily Paleozoic and Mesozoic eras). Lithification occurs through compaction and cementation of calcium carbonate.

Uses & Applications

Widely used in construction (aggregate, cement production, building stone), agriculture (soil conditioner), and as a chemical feedstock for industrial lime production.

Geological Facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary parent rock for Karst landscapes, where water creates caves, sinkholes, and underground rivers.

Field Identification & Locations

Identify in the field using the 'acid test'—it will effervesce (fizz) when a drop of dilute hydrochloric acid is applied. Look for fine grains, earthy texture, and occasional fossil inclusions. Extremely common globally.

Identified on: 4/25/2026

Mode: Standard