sedimentary

Limestone

CaCO3 (Calcium Carbonate)

Hardness: 3-4 (Mohs scale), Color: light grey to tan, Luster: dull to earthy, Crystal structure: Trigonal (microcrystalline), Cleavage: none, Specific gravity: 2.3-2.7

Identified July 19, 2026More sedimentary →

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Physical properties

Hardness: 3-4 (Mohs scale), Color: light grey to tan, Luster: dull to earthy, Crystal structure: Trigonal (microcrystalline), Cleavage: none, Specific gravity: 2.3-2.7

Formation & geological history

Formed in warm, shallow marine environments from the accumulation of shell, coral, algal, and fecal debris. This specimen appears water-worn, likely found in a river or coastal area.

Uses & applications

Used primarily in construction as aggregate, for making cement, as a flux in steel production, and as an agricultural soil conditioner.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is highly susceptible to acid rain, which creates caves and sinkholes over geological time.

Field identification & locations

Can be identified by a 'fizz' test (effervescence) when a small drop of diluted hydrochloric acid or vinegar is applied. Commonly found in ancient sea beds and riverbanks.