sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 (Mohs scale), Color: tan, grey, or yellowish. Luster: dull/earthy. Crystal structure: Trigonal (microcrystalline). Will fizz with weak acid.

Hardness: 3 (Mohs scale), Color: tan, grey, or yellowish
Color: tan, grey, or yellowish
Luster: dull/earthy

Identified July 15, 2026More sedimentary →

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Physical properties

Hardness: 3 (Mohs scale), Color: tan, grey, or yellowish. Luster: dull/earthy. Crystal structure: Trigonal (microcrystalline). Will fizz with weak acid.

Formation & geological history

Formed in marine environments through the accumulation of shell, coral, algal, and fecal debris. Most common in shallow, warm sea waters.

Uses & applications

Used as a major building material, in the manufacture of cement, as an aggregate for road bases, and for neutralizing acidic soils.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary rock type hosting spectacular cave systems like Mammoth Cave.

Field identification & locations

Identify in the field by its softness relative to steel and its reaction (effervescence) when exposed to a drop of vinegar or diluted hydrochloric acid.