sedimentary

Limestone

Calcium Carbonate (CaCO3)

AI-generated identification · may be incorrect

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

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

Identified July 18, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: white, grey, or tan; 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 clear, warm, shallow marine waters. Can also form through chemical precipitation from lake or ocean water.

Uses & applications

Used extensively in construction (as gravel, cement, and dimension stone), agriculture (soil conditioner), and in the production of glass and steel.

Geological facts

Limestone or marble represent about 10% of the total volume of all sedimentary rocks. It is the primary material found in caves, where it is slowly dissolved by carbonic acid to create stalactites and stalagmites.

Field identification & locations

Can be identified by its relative softness (scratched by a copper penny or steel knife) and its reaction to dilute hydrochloric acid (it will fizz or effervesce). Common in riverbeds and ancient seafloors.