sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Light gray to tan; Luster: Dull/Earthy; Crystal Structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral in calcite crystals; Specific Gravity: 2.5-2.7

Hardness: 3 on Mohs scale
Color: Light gray to tan
Luster: Dull/Earthy

Identified April 20, 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: Light gray to tan; Luster: Dull/Earthy; Crystal Structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral in calcite crystals; Specific Gravity: 2.5-2.7

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 ocean water or cave water.

Uses & applications

Used extensively in construction as aggregate, in cement manufacturing, as a soil conditioner in agriculture, and as a flux in steel production.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary rock type found in karst landscapes, which are characterized by caves and sinkholes.

Field identification & locations

Identify in the field by applying a drop of dilute hydrochloric acid; it will effervesce (fizz) vigorously. It is often found in bedded layers and may contain visible fossils.