mineral

Calcite

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: typically white, clear, or off-white; Luster: vitreous to pearly; Crystal structure: Trigonal (often rhombohedral); Cleavage: Perfect rhombohedral in three directions; Specific Gravity: 2.71

Hardness: 3 on Mohs scale
Color: typically white, clear, or off-white
Luster: vitreous to pearly

Identified March 8, 2026More mineral →

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Physical properties

Formation & geological history

Formed through both chemical precipitation and biological activity. It is a primary constituent of sedimentary rocks like limestone and marble (metamorphic), often appearing in hydrothermal veins or as deposits in caves (stalactites/stalagmites).

Uses & applications

Used widely in the construction industry for making cement and mortar, as a soil conditioner in agriculture, a pigment in paint, and occasionally as a flux in steel manufacturing. High-purity specimens are used in optical instruments.

Geological facts

Calcite exhibits double refraction; if you place a clear piece over a line of text, you will see two lines. It is also the primary component of sea shells and coral reefs.

Field identification & locations

Can be identified in the field by its extreme reactivity to dilute hydrochloric acid (it will fizz/effervesce). Its rhombohedral cleavage is a key visual marker. Found globally, frequently in limestone quarries or mountain regions.