mineral

Optical Calcite

CaCO3 (Calcium Carbonate)

Hardness: 3 on the Mohs scale, Color: Colorless or very pale tints, Luster: Vitreous to pearly, Crystal structure: Trigonal (rhombohedral cleavage), Specific gravity: 2.71

Identified August 3, 2026More mineral →

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Physical properties

Hardness: 3 on the Mohs scale, Color: Colorless or very pale tints, Luster: Vitreous to pearly, Crystal structure: Trigonal (rhombohedral cleavage), Specific gravity: 2.71

Formation & geological history

Forms in sedimentary environments, often from marine organisms' shells or precipitated from calcium-rich waters. Also found in hydrothermal veins and metamorphic rocks like marble.

Uses & applications

Used historically in optical instruments due to its strong double refraction. Now primarily a collector's item and used in education to demonstrate birefringence.

Geological facts

Also known as Iceland Spar. Famous for its double refraction property, where looking through a clear piece will show a doubled image.

Field identification & locations

Easily identified by its rhombohedral shape (often cleaves into perfect rhombohedrons) and double refraction. Will effervesce (fizz) in weak hydrochloric acid.