sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: typically white, gray, or tan; Luster: dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral in calcite particles; Specific gravity: 2.3 to 2.7.

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

Identified March 22, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed primarily in shallow marine environments from the accumulation of shell, coral, algal, and fecal debris. It can also form chemically through the precipitation of calcium carbonate from lake or ocean water.

Uses & applications

Extensively used as a building material, in the manufacture of cement, as an aggregate for the base of roads, as white pigment or filler in products such as toothpaste or paints, and as a soil conditioner in agriculture.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks on Earth. Most of the world's caves are located in limestone formations due to the rock's solubility in slightly acidic rainwater.

Field identification & locations

Identify in the field by its softness (can be scratched by a copper coin) and its immediate effervescence (fizzing) when in contact with a drop of dilute hydrochloric acid or strong vinegar. Found globally in ancient seabed deposits.