Limestone

Physical Properties

Hardness: 3 (Mohs scale), Color: White, grey, or tan, Luster: Dull to earthy, Crystal Structure: Trigonal (as calcite), Cleavage: Perfect rhombohedral, Specific Gravity: 2.7

Formation & Geological History

Formed in marine environments through the accumulation of shell, coral, algal, and fecal debris. It can also form through chemical precipitation from lake or ocean water.

Uses & Applications

Primary source of lime for cement, used as a building stone (dimension stone), aggregate for road bases, and as a soil conditioner in agriculture.

Geological Facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary rock found in karst landscapes, which are characterized by caves and sinkholes.

Field Identification & Locations

Can be identified in the field by its softness (can be scratched by a copper coin) and its strong effervescent reaction to dilute hydrochloric acid. Commonly found in thick beds around the world.

Identified on: 4/25/2026

Mode: Standard