sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on the Mohs scale; Color: typically grey, tan, or white; Luster: dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: perfect rhombohedral; Specific gravity: 2.7.

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

Identified March 21, 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 the Mohs scale; Color: typically grey, tan, or white; Luster: dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: perfect rhombohedral; Specific gravity: 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 calcium-rich waters in caves or hot springs. Geological age varies from Precambrian to Holocene.

Uses & applications

Extensively used in construction as building stone, road base, and a primary ingredient in cement/concrete. Used in agriculture to neutralize soil acidity, and in the chemical industry for steel manufacturing and glass making.

Geological facts

Limestone is the source of approximately 10% of all sedimentary rocks. Many of the world's most famous landmarks, including the Great Pyramids of Giza and the Parthenon, are constructed primarily from limestone.

Field identification & locations

Can be identified in the field using the 'acid test'—it will effervesce (fizz) when a drop of diluted hydrochloric acid or strong vinegar is applied. Commonly found in areas that were once ancient sea beds. Check for fossil inclusions to confirm organic origin.