sedimentary

Limestone

Calcium carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: light grey to cream; Luster: dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: rhombohedral (rarely visible in hand sample); Specific gravity: 2.3–2.7

Hardness: 3 on Mohs scale
Color: light grey to cream
Luster: dull to earthy

Identified April 13, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed primarily from the accumulation of shell, coral, algal, and fecal debris in warm, shallow marine waters. Can also form through precipitation from calcium-rich water.

Uses & applications

Major use in construction as aggregate, manufacture of cement, soil conditioner in agriculture, and as a flux in steel making.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary source for karst landscapes, creating massive cave systems and sinkholes through acidity in rainwater.

Field identification & locations

Identify in the field using the 'acid test'—it will fizz (effervesce) when a small drop of diluted hydrochloric acid is applied. Commonly found in areas with past or present marine environments.