sedimentary

Limestone

Calcium Carbonate (CaCO3)

AI-generated identification · may be incorrect

Hardness: 3-4 (Mohs scale); Color: Gray, tan, or white; Luster: Dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific gravity: 2.7.

Hardness: 3-4 (Mohs scale)
Color: Gray, tan, or white
Luster: Dull to earthy

Identified July 1, 2026More sedimentary →

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Physical properties

Hardness: 3-4 (Mohs scale); Color: Gray, tan, or white; 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 via precipitation of calcium carbonate from lake or ocean water.

Uses & applications

Used primarily as raw material for cement, building stone, aggregate for road bases, and as a flux in steel manufacturing. It is also ground for agricultural use.

Geological facts

Limestone covers about 10% of the Earth's land surface. It is often the primary component of caves and karst landscapes due to its solubility in weak acids.

Field identification & locations

Identify in the field by applying a drop of dilute hydrochloric acid; it will effervesce (fizz). Look for visible fossils or shell fragments. Commonly found in large deposits across the Midwestern USA and Europe.