mineral

Calcite (Optical or Clear Calcite)

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Clear to white; Luster: Vitreous/Glassy; Crystal Structure: Trigonal/Rhombohedral; Cleavage: Perfect rhombohedral in three directions; Specific Gravity: 2.71

Hardness: 3 on Mohs scale
Color: Clear to white
Luster: Vitreous/Glassy

Identified June 1, 2026More mineral →

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Physical properties

Hardness: 3 on Mohs scale; Color: Clear to white; Luster: Vitreous/Glassy; Crystal Structure: Trigonal/Rhombohedral; Cleavage: Perfect rhombohedral in three directions; Specific Gravity: 2.71

Formation & geological history

Formed through chemical precipitation in sedimentary environments, hydrothermal veins, or as a primary mineral in igneous carbonatites. It is often found in limestone and marble deposits.

Uses & applications

Used in the manufacture of cement and mortar, as a soil conditioner in agriculture, in the optical industry (for polarizing prisms), and as a decorative collector specimen.

Geological facts

Calcite exhibits double refraction (birefringence); if you place a clear piece over text, the letters appear doubled. It is the primary constituent of stalactites and stalagmites in caves.

Field identification & locations

Identify in the field using a 'fizz test' with dilute hydrochloric acid; it will effervesce vigorously. Look for the characteristic rhombohedral 'leaning box' shape and low hardness (can be scratched by a copper penny).

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