sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 (Mohs scale); Color: Tan, beige, or white; Luster: Dull/earthy; Crystal Structure: Trigonal (often microscopic calcite); Cleavage: Perfect rhombohedral in calcite crystals, usually not visible in massive form; Specific Gravity: 2.5–2.7

Hardness: 3 (Mohs scale)
Color: Tan, beige, or white
Luster: Dull/earthy

Identified May 30, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in marine environments through 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. Most deposits range from the Paleozoic era to the present.

Uses & applications

Widely used in construction as an aggregate for road bases and concrete, as a building stone (facades), in the manufacture of cement, and in agriculture as limestone to neutralize soil acidity.

Geological facts

Limestone covers about 10% of the Earth's total land surface. It is the primary rock found in karst landscapes, leading to the formation of extensive cave systems like Mammoth Cave.

Field identification & locations

Identify in the field by its light color and reaction to dilute hydrochloric acid (it will fizz). Commonly found in ancient sea beds, cliff faces, and quarries. Collectors look for fossil inclusions which are common in this rock.