mineral

Calcite with Quartz coating

Calcium Carbonate (CaCO3) with Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 3 (Calcite body) and 7 (Quartz crust); Color: White to yellowish-tan; Luster: Vitreous to pearly; Crystal structure: Trigonal/Hexagonal; Cleavage: Perfect rhombohedral in the calcite base.

Hardness: 3 (Calcite body) and 7 (Quartz crust)
Color: White to yellowish-tan
Luster: Vitreous to pearly

Identified June 1, 2026More mineral →

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Physical properties

Hardness: 3 (Calcite body) and 7 (Quartz crust); Color: White to yellowish-tan; Luster: Vitreous to pearly; Crystal structure: Trigonal/Hexagonal; Cleavage: Perfect rhombohedral in the calcite base.

Formation & geological history

Formed through hydrothermal precipitation in veins or sedimentary environments where calcium-rich fluids crystallize, followed by a secondary silica-rich fluid deposition that creates the drusy quartz layer.

Uses & applications

Used primarily as a collector's specimen. Calcite is used in manufacture of cement and lime, while quartz is used in electronics and glass-making.

Geological facts

The specimen shows 'drusy' quartz, which is a coating of fine crystals on a mineral surface. Calcite is one of the most common minerals on Earth and can double-refract light.

Field identification & locations

Identify by testing the white base with dilute acid (it will fizz) and checking hardness of the top layer (it will scratch glass). Common in limestone quarries and hydrothermal vein deposits worldwide.