mineral
Polished brown calcite (likely honey calcite)
Calcite, calcium carbonate (CaCO₃)
AI-generated identification · may be incorrectTan-to-brown, translucent to opaque, with a polished vitreous-to-waxy surface and internal white cleavage/fracture zones. Calcite has Mohs hardness 3, rhombohedral crystal structure, perfect rhombohedral cleavage, and specific gravity about 2.71; it should fizz with dilute hydrochloric acid or strong vinegar (slowly).
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Physical properties
Tan-to-brown, translucent to opaque, with a polished vitreous-to-waxy surface and internal white cleavage/fracture zones. Calcite has Mohs hardness 3, rhombohedral crystal structure, perfect rhombohedral cleavage, and specific gravity about 2.71; it should fizz with dilute hydrochloric acid or strong vinegar (slowly).
Formation & geological history
Forms in limestone, hydrothermal veins, cavities, and carbonate-rich pegmatitic or sedimentary environments. The specimen appears tumbled or cabochon-polished; its exact age cannot be determined visually.
Uses & applications
Mostly sold as a decorative or lapidary stone, carving material, and mineral specimen; not generally suitable for durable jewelry because it scratches easily and reacts with acids.
Geological facts
Brown coloration commonly comes from iron-bearing impurities or inclusions. The pale patches likely expose cleavage planes or cloudy carbonate zones rather than separate crystals.
Field identification & locations
Identification is uncertain from the photograph alone; test hardness against a copper coin (calcite scratches easily) and acid reaction, while avoiding damage to the polished face. Calcite is common in southeastern Brazil, including Minas Gerais, so the reported location is plausible.
