mineral
Likely aragonite crystal cluster
Aragonite, CaCO₃
AI-generated identification · may be incorrectSmall reddish-brown radiating/acicular crystals with vitreous to resinous luster; orthorhombic structure, Mohs hardness 3.5–4, imperfect cleavage, and specific gravity about 2.94. The color may result from iron staining or surface coating.
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Physical properties
Small reddish-brown radiating/acicular crystals with vitreous to resinous luster; orthorhombic structure, Mohs hardness 3.5–4, imperfect cleavage, and specific gravity about 2.94. The color may result from iron staining or surface coating.
Formation & geological history
Aragonite forms at low temperatures in cavities, hot-spring deposits, evaporites, caves, and biological shells; most specimens are geologically young, though aragonite can occur in rocks of any age. The image resolution limits identification certainty.
Uses & applications
Used mainly as a collector mineral and occasionally as an ornamental or aquarium material; it is not typically used as a gemstone because it is soft and unstable relative to calcite.
Geological facts
Aragonite is a polymorph of calcite: both have the formula CaCO₃ but different crystal structures. It can slowly transform into calcite over geological time, especially under surface conditions.
Field identification & locations
Look for radiating needle-like crystals and distinguish it from calcite by crystal habit; a dilute acid test produces effervescence, but avoid damaging a valuable specimen. Common localities include Spain, Morocco, Mexico, Austria, and the Bahamas.
