sedimentary

Limestone

Calcium carbonate (CaCO3)

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

Hardness: 3 (Mohs scale)
Color: White, gray, or tan
Luster: Dull to earthy

Identified May 15, 2026More sedimentary →

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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.