sedimentary

Limestone

Limestone (Calcium Carbonate: CaCO3)

Hardness: 3 on Mohs scale; Color: typically gray, tan, or white; Luster: dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Rhombohedral (microscopic)

Hardness: 3 on Mohs scale
Color: typically gray, tan, or white
Luster: dull to earthy

Identified June 1, 2026More sedimentary →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 3 on Mohs scale; Color: typically gray, tan, or white; Luster: dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Rhombohedral (microscopic)

Formation & geological history

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

Uses & applications

Used extensively in construction as road base, aggregate, and a key ingredient in cement/concrete. Also used as a soil conditioner and in glass making.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary rock found in cavern systems and often contains visible fossils.

Field identification & locations

Can be identified in the field by its softness (easily scratched by a steel nail) and its rapid effervescence (bubbling) when exposed to a drop of dilute hydrochloric acid.