mineral

Calcite

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Colorless to white/pale yellow; Luster: Vitreous to pearly; Crystal Structure: Trigonal (Rhombohedral); Cleavage: Perfect in three directions; Specific Gravity: 2.71

Hardness: 3 on Mohs scale
Color: Colorless to white/pale yellow
Luster: Vitreous to pearly

Identified July 11, 2026More mineral →

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Physical properties

Hardness: 3 on Mohs scale; Color: Colorless to white/pale yellow; Luster: Vitreous to pearly; Crystal Structure: Trigonal (Rhombohedral); Cleavage: Perfect in three directions; Specific Gravity: 2.71

Formation & geological history

Formed primarily by chemical precipitation in marine environments or through biological activity (shells). It also forms in hydrothermal veins and hot springs. It is a major constituent of sedimentary rocks such as limestone and metamorphic rocks like marble.

Uses & applications

Used widely in construction (cement and concrete), as a soil conditioner in agriculture, as an abrasive, and in the chemical industry. Clear 'Iceland Spar' varieties are used for optical purposes due to double refraction.

Geological facts

Calcite exhibits a unique property called double refraction; if you look through a clear crystal, images appear doubled. It will react and fizz (effervesce) immediately when in contact with weak hydrochloric acid.

Field identification & locations

Collectors should look for the characteristic rhombohedral cleavage at near-75 degree angles. It is found globally, with famous localities in Mexico, China, and the USA. It is easily scratched by a copper penny or a pocket knife.