mineral

Calcite crystal cluster

Calcite (calcium carbonate, CaCO₃)

AI-generated identification · may be incorrect

White to honey-yellow, translucent-to-opaque crystals with a vitreous to pearly luster; Mohs hardness 3, rhombohedral crystal structure, perfect rhombohedral cleavage, and specific gravity about 2.71. The granular, cream-colored appearance is consistent with calcite, though image-only identification is approximate.

Identified August 23, 2026More mineral →

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Physical properties

Formation & geological history

Forms when calcium-rich groundwater precipitates in caves, veins, cavities, and sedimentary rocks; the yellow color may result from iron or other impurities. Calcite occurs from Precambrian to modern deposits, with no age determinable from the specimen.

Uses & applications

Used to manufacture cement, lime, aggregates, and agricultural soil amendments; clear optical calcite is collectible, while ordinary clusters have modest specimen value.

Geological facts

Calcite effervesces visibly in dilute hydrochloric acid and shows strong birefringence—printed text viewed through a clear fragment may appear doubled.

Field identification & locations

Common worldwide, including Mexico, the United States, Iceland, and China. Identify it by rhombohedral cleavage, softness, and acid reaction; distinguish from quartz, which is harder and does not fizz.