mineral

Calcite crystal cluster

Calcite (calcium carbonate, CaCO₃)

AI-generated identification · may be incorrect

Likely pale honey-brown, translucent calcite with a glassy to pearly luster and prominent rhombohedral cleavage; Mohs hardness 3, trigonal crystal system, and specific gravity about 2.71. The irregular cluster may include minor matrix or iron staining.

Identified September 13, 2026More mineral →

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Physical properties

Formation & geological history

Calcite commonly precipitates from groundwater and hydrothermal fluids in cavities, veins, limestone, and geodes. Its age cannot be determined from the photograph; specimens form in environments ranging from recent cave deposits to ancient sedimentary and volcanic rocks.

Uses & applications

Used industrially in cement, lime, aggregate, glass, and chemical production; clear crystals are collector specimens. Jewelry use is limited because calcite is soft and cleaves easily.

Geological facts

Calcite strongly effervesces with dilute hydrochloric acid and commonly shows double refraction through clear pieces. Its cleavage fragments are typically rhombohedral rather than cubic.

Field identification & locations

Identify it by testing hardness against a copper coin or fingernail, observing rhombohedral cleavage, and applying a tiny acid test to an inconspicuous spot. Common localities include Mexico, Iceland, the United States, Peru, and China.