mineral

Calcite with iron staining

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: white/cream with brownish-yellow iron oxide staining; Luster: Vitreous to pearly; Crystal structure: Trigonal (rhombohedral cleavage); Cleavage: Perfect rhombohedral in three directions; Specific gravity: 2.71

Hardness: 3 on Mohs scale
Color: white/cream with brownish-yellow iron oxide staining
Luster: Vitreous to pearly

Identified March 16, 2026More mineral →

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Physical properties

Formation & geological history

Formed through chemical precipitation in sedimentary environments or hydrothermal veins. This specimen likely represents secondary mineralization or a vein-filling formation, potentially dating from any point from the Proterozoic to the Holocene depending on the local geology.

Uses & applications

Used in the manufacture of cement and mortar, as a soil conditioner in agriculture, a pigment in paint, and as a source of calcium in pharmaceuticals. High-clarity specimens are used in optical instruments.

Geological facts

Calcite is famous for its double refraction (birefringence), where light passing through a clear specimen splits into two rays. It is also the primary component of limestone and marble.

Field identification & locations

Identify in the field using the 'acid test'—it will effervesce (fizz) vigorously when a drop of dilute hydrochloric acid or strong vinegar is applied. It can be scratched easily with a copper penny. Commonly found in sedimentary basins and limestone caverns worldwide.

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