mineral

Calcite Geode

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: honey-yellow, white, or colorless; Luster: Vitreous to pearly; Crystal structure: Trigonal/Rhombohedral; Cleavage: Perfect rhombohedral in three directions.

Hardness: 3 on Mohs scale
Color: honey-yellow, white, or colorless
Luster: Vitreous to pearly

Identified May 7, 2026More mineral →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 3 on Mohs scale; Color: honey-yellow, white, or colorless; Luster: Vitreous to pearly; Crystal structure: Trigonal/Rhombohedral; Cleavage: Perfect rhombohedral in three directions.

Formation & geological history

Formed via precipitation of calcium carbonate from mineral-rich hydrothermal fluids or groundwater within cavities of sedimentary rocks like limestone or dolomite. Often found in vugs or host rock cavities.

Uses & applications

Industrial use in cement, lime, and soil treatment. Transparent varieties are used in optical instruments. Collector specimens are popular for display and educational purposes.

Geological facts

Calcite is known for its property of double refraction, where a single beam of light entering the crystal is split into two. It also reacts vigorously with cold dilute hydrochloric acid.

Field identification & locations

Identify by its rhombohedral cleavage and relative softness (scratched by a copper penny but not a fingernail). Frequently found in limestone quarries or karst landscapes worldwide.