mineral

White calcite specimen

Calcite (calcium carbonate, CaCO₃)

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Identified August 30, 2026More mineral →

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Physical properties

White to translucent, pearly-to-glassy luster with irregular cleavage surfaces; calcite is Mohs hardness 3, has perfect rhombohedral cleavage, trigonal crystal symmetry, and specific gravity about 2.71. The blocky shape and pale brown coating are consistent with calcite, though the photograph alone cannot confirm it over gypsum or quartz.

Formation & geological history

Usually forms from carbonate-rich groundwater, hydrothermal fluids, caves, or limestone cavities; many specimens are geologically young relative to their host rock. It commonly precipitates as veins, crystalline masses, stalactites, and cavity coatings.

Uses & applications

Used extensively in cement, lime, aggregate, soil treatment, and chemical manufacture; clear optical calcite is collectible, while ordinary white pieces have little commercial value.

Geological facts

The decisive field test is vigorous fizzing in cold dilute hydrochloric acid or vinegar, though vinegar may react slowly. Calcite commonly shows rhombohedral cleavage and can be scratched by a copper coin or steel knife.

Field identification & locations

Common worldwide in limestone regions, hydrothermal veins, and cave deposits; major sources include Mexico, Iceland, the United States, and China. Confirm identity with acid reaction, cleavage, and hardness tests.