mineral

Calcite specimen

Calcite (calcium carbonate, CaCO₃)

AI-generated identification · may be incorrect

White to cream, translucent-to-opaque mineral with a vitreous to pearly luster; Mohs hardness 3, perfect rhombohedral cleavage, and commonly rhombohedral or scalenohedral crystals. It reacts vigorously with dilute hydrochloric acid and has specific gravity about 2.71.

Identified August 19, 2026More mineral →

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Physical properties

Formation & geological history

Forms by precipitation from groundwater, hydrothermal fluids, and marine or cave environments; it is also the principal mineral in limestone and marble. The specimen’s exact geological age cannot be determined from the image.

Uses & applications

Used in cement, lime, aggregate, glass manufacture, soil treatment, and fillers; clear crystals are collected but generally have limited jewelry use because of low hardness.

Geological facts

Calcite is strongly birefringent, producing double images through clear crystals, and occurs in more than 600 crystal forms. Its cleavage fragments commonly break into distinctive rhombohedra rather than cubes.

Field identification & locations

Likely identifiable by its soft, easily scratched surface, rhombohedral cleavage, and acid fizz; common worldwide, especially in limestone caves, veins, and sedimentary basins. Avoid acid testing on valuable specimens and use a hidden spot.