sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 (Mohs scale); Color: White, gray, tan, or cream; Luster: Dull to earthy; Texture: Fine to medium-grained; Reacts strongly to diluted hydrochloric acid.

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

Identified July 18, 2026More sedimentary →

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Physical properties

Hardness: 3 (Mohs scale); Color: White, gray, tan, or cream; Luster: Dull to earthy; Texture: Fine to medium-grained; Reacts strongly to diluted hydrochloric acid.

Formation & geological history

Formed in marine environments from the accumulation of shell, coral, algal, and fecal debris. It can also form through chemical precipitation from ocean water.

Uses & applications

Widely used as a construction material (dimension stone), in the manufacture of cement, as a soil conditioner in agriculture, and as a flux in steel making.

Geological facts

Limestone covers about 10% of the total surface area of the Earth. Many famous caves, such as Mammoth Cave, are formed in limestone beds through the dissolution of the rock by acidic groundwater.

Field identification & locations

Identify in the field by its light color and by testing with a drop of vinegar or acid (it will fizz). Commonly found in areas that were once prehistoric seafloors.