sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: tan, grey, or white; Luster: dull to earthy; Crystal Structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific Gravity: 2.5-2.7

Hardness: 3 on Mohs scale
Color: tan, grey, or white
Luster: dull to earthy

Identified April 20, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: tan, grey, or white; Luster: dull to earthy; Crystal Structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific Gravity: 2.5-2.7

Formation & geological history

Formed primarily from the accumulation of shell, coral, algal, and fecal debris in warm, shallow marine waters. Can also be formed by the chemical precipitation of calcium carbonate from lake or ocean water.

Uses & applications

Used extensively in construction as building stone, road base, and a primary ingredient in Portland cement. Also used as a soil conditioner in agriculture and as a filler in toothpaste and plastics.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary rock type in which most of the world's caves are formed through chemical weathering.

Field identification & locations

Identify in the field by its effervescence (bubbling) when a drop of dilute hydrochloric acid is applied. Look for fossils or a fine-grained, chalky texture. Commonly found in former marine basins.