sedimentary

Limestone

Calcium Carbonate (CaCO3)

AI-generated identification · may be incorrect

Hardness: 3-4 (Mohs); Color: Gray, tan, white, or light brown; Luster: Dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Rhombohedral (microscopic); Specific gravity: 2.7

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

Identified June 29, 2026More sedimentary →

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Physical properties

Hardness: 3-4 (Mohs); Color: Gray, tan, white, or light brown; Luster: Dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Rhombohedral (microscopic); Specific gravity: 2.7

Formation & geological history

Formed in marine environments through the accumulation of shell, algal, and fecal debris. It can also form via chemical precipitation from calcium-rich water.

Uses & applications

Used extensively in construction as aggregate, in cement production, as a building stone (facing), and in agriculture to neutralize soil acidity.

Geological facts

Limestone often contains well-preserved fossils. It is the primary component of most cave systems through the process of dissolution by slightly acidic groundwater.

Field identification & locations

Identify by testing with a drop of dilute hydrochloric acid; it will effervesce (fizz) vigorously. It is commonly found in sedimentary basins and ancient sea beds worldwide.