mineral

Calcite crystal (likely Iceland spar)

Calcite, calcium carbonate (CaCO₃)

AI-generated identification · may be incorrect

Pale gray-white, translucent, vitreous to pearly luster; commonly rhombohedral cleavage and trigonal crystal structure. Mohs hardness 3, specific gravity about 2.71; the blocky shape and strong cleavage are characteristic.

Identified September 15, 2026More mineral →

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Physical properties

Formation & geological history

Forms in limestones, hydrothermal veins, caves, and evaporite settings through precipitation from calcium-rich fluids. Calcite occurs from ancient sedimentary deposits to modern cave growth; the image alone cannot establish age or locality.

Uses & applications

Used in cement, lime, construction aggregate, metallurgy, and chemical processing; clear Iceland spar is collected for its optical double refraction. Common specimens have modest value unless exceptionally transparent or well formed.

Geological facts

Iceland spar is unusually clear calcite that produces double images because light follows two optical paths through the crystal.

Field identification & locations

Test with a steel knife or copper coin only cautiously: calcite scratches easily and fizzes vigorously with dilute hydrochloric acid; rhombohedral cleavage and double refraction are diagnostic. Common worldwide, especially in limestone regions and hydrothermal veins.