sedimentary

Limestone

Sedimentary Calcium Carbonate (CaCO3)

Hardness: 3 (Mohs scale), Color: tan or grayish-buff, Luster: dull to earthy, Crystal Structure: Trigonal (microcrystalline), Cleavage: none, Specific Gravity: 2.5-2.7

Identified July 15, 2026More sedimentary →

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Physical properties

Hardness: 3 (Mohs scale), Color: tan or grayish-buff, Luster: dull to earthy, Crystal Structure: Trigonal (microcrystalline), Cleavage: none, Specific Gravity: 2.5-2.7

Formation & geological history

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

Uses & applications

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

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. Most caves are formed in limestone when acidic groundwater dissolves the rock over thousands of years.

Field identification & locations

Identify in the field by its softness (can be scratched by a copper coin) and its effervescence (bubbling) when a drop of weak hydrochloric acid or vinegar is applied. Commonly found in areas that were once prehistoric seafloors.