mineral

Clear calcite (optical calcite)

Calcite, CaCO₃

AI-generated identification · may be incorrect

Colorless to pale honey, translucent, vitreous to pearly luster; trigonal crystal structure with prominent rhombohedral cleavage. Mohs hardness 3; commonly shows double refraction, though this rough specimen’s clarity and shape limit confirmation.

Identified October 15, 2026More mineral →

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Physical properties

Formation & geological history

Forms in sedimentary limestone and marble, hydrothermal veins, and caves; calcite occurs from ancient deposits to actively forming settings. The specimen’s exact age and origin cannot be determined from appearance alone.

Uses & applications

Used in cement and lime production, building stone, soil treatment, and optical instruments; clear pieces are collected and sometimes used for demonstrations or decor.

Geological facts

Calcite reacts with dilute acid by effervescing and is much softer than quartz. Iceland spar, a clear variety, historically enabled experiments demonstrating double refraction.

Field identification & locations

Look for rhombohedral cleavage and test cautiously with dilute acid or a copper coin; common worldwide in limestone regions, caves, and veins. The pictured piece appears to be a rough translucent calcite fragment.