sedimentary

Limestone

Sedimentary Calcium Carbonate (CaCO3)

Hardness: 3 (Mohs scale); Color: Gray, tan, or white with green algae growth; Luster: Dull/earthy; Crystal structure: Trigonal (microcrystalline); Specific gravity: 2.5-2.7

Hardness: 3 (Mohs scale)
Color: Gray, tan, or white with green algae growth
Luster: Dull/earthy

Identified July 21, 2026More sedimentary →

Explore Limestone in the encyclopedia →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 3 (Mohs scale); Color: Gray, tan, or white with green algae growth; Luster: Dull/earthy; Crystal structure: Trigonal (microcrystalline); Specific gravity: 2.5-2.7

Formation & geological history

Formed by the accumulation of shell, coral, algal, and fecal debris in marine environments. It can also form chemically through the precipitation of calcium carbonate from lake or ocean water. Most deposits range from the Paleozoic to Mesozoic eras.

Uses & applications

Used extensively as a building material, aggregate for concrete, raw material for making cement, and as a soil conditioner in agriculture.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks on Earth. It often contains fossils of ancient marine life and is the primary rock type in karst landscapes where caves and sinkholes form.

Field identification & locations

Identified in the field by its softness (can be scratched by a copper penny/knife) and its effervescence (bubbling) when a drop of weak hydrochloric acid is applied. It is commonly found in road cuts and near water bodies.