Limestone

Physical Properties

Hardness: 3 (Mohs scale); Color: White, gray, or tan; Luster: Dull to earthy; Crystal structure: Trigonal (rhombohedral); Cleavage: Perfect rhombohedral (in calcite crystals); Specific gravity: 2.7

Formation & Geological History

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

Uses & Applications

Used widely in construction (aggregate, cement making), as a soil conditioner in agriculture, and as a decorative stone in architecture and landscaping.

Geological Facts

Limestone or chalk comprises about 10% of the total volume of all sedimentary rocks. It is the source of material for many of the world's most famous caves and karst landscapes.

Field Identification & Locations

Identify in the field by its softness (scratched by a copper penny) and its effervescence (fizzing) when in contact with dilute hydrochloric acid or strong vinegar. Commonly found in coastal areas and riverbeds.

Identified on: 5/15/2026

Mode: Standard