mineral
Tumbled amethyst
Quartz, purple variety; silicon dioxide (SiO₂) colored mainly by iron-related defects
AI-generated identification · may be incorrectMohs hardness 7; purple to violet, vitreous luster, translucent, trigonal crystal structure, and no cleavage but conchoidal fracture. The rounded surface indicates tumbling/polishing.
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Physical properties
Mohs hardness 7; purple to violet, vitreous luster, translucent, trigonal crystal structure, and no cleavage but conchoidal fracture. The rounded surface indicates tumbling/polishing.
Formation & geological history
Amethyst forms when iron-bearing quartz crystallizes in gas cavities and fractures of volcanic rocks, commonly basalt, with later irradiation producing the purple color. Most specimens formed during the Cenozoic or older volcanic episodes, depending on locality.
Uses & applications
Used for inexpensive jewelry, carvings, ornamental pieces, and mineral collections. This small tumbled specimen has modest commercial value.
Geological facts
Color can fade with prolonged heat or strong sunlight; heating may convert it to yellow citrine. Amethyst is February’s birthstone and a common quartz variety.
Field identification & locations
Identify by its glassy luster, hardness, conchoidal fracture, and purple zoning; unlike purple glass, it will scratch glass and usually shows natural color variation. Common sources include Brazil, Uruguay, Zambia, and Mexico.
