sedimentary

Limestone

Sedimentary rock composed primarily of Calcium Carbonate (CaCO3)

AI-generated identification · may be incorrect

Hardness: 3-4 (Mohs scale); Color: White, tan, gray; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline calcite); Cleavage: Rhombohedral (microscopic); Specific gravity: 2.3-2.7

Hardness: 3-4 (Mohs scale)
Color: White, tan, gray
Luster: Dull to earthy

Identified July 1, 2026More sedimentary →

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Physical properties

Hardness: 3-4 (Mohs scale); Color: White, tan, gray; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline calcite); Cleavage: Rhombohedral (microscopic); Specific gravity: 2.3-2.7

Formation & geological history

Formed primarily in marine environments from the accumulation of shell, coral, algal, and fecal debris. It can also be formed by the precipitation of calcium carbonate from lake or ocean water.

Uses & applications

Used extensively in construction as road base, aggregate, and building stone. It is a key ingredient in portland cement and is used as a soil conditioner in agriculture.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. Most of the world's caves are formed in limestone because it is soluble in slightly acidic groundwater.

Field identification & locations

Can be identified in the field by the 'acid test': it will effervesce (fizz) when a drop of dilute hydrochloric acid is applied. Look for fossil remains which are common in many limestone layers.