mineral
Amethyst geode
Quartz, SiO₂; purple variety amethyst, commonly a drusy-lined geode
AI-generated identification · may be incorrectHardness 7 Mohs; purple to lilac quartz crystals with vitreous luster, conchoidal fracture, and no cleavage. The specimen appears polished or cut, with a pale quartz/chalcedony rim and crystalline amethyst interior.
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Physical properties
Hardness 7 Mohs; purple to lilac quartz crystals with vitreous luster, conchoidal fracture, and no cleavage. The specimen appears polished or cut, with a pale quartz/chalcedony rim and crystalline amethyst interior.
Formation & geological history
Forms when silica-rich groundwater deposits quartz crystals inside gas cavities in volcanic basalt, typically over millions of years; Brazilian and Uruguayan geodes commonly formed in Mesozoic volcanic rocks.
Uses & applications
Used for mineral collecting, display, lapidary décor, and occasionally jewelry; large attractive geodes can be valuable, while common polished pieces are widely available.
Geological facts
Purple color results mainly from iron impurities and natural irradiation; heating can turn amethyst yellow or orange, producing citrine-like material.
Field identification & locations
Identify by purple transparent-to-translucent quartz crystals, glassy luster, and hardness sufficient to scratch ordinary glass; avoid confusing it with dyed quartz or glass. Common sources include Brazil, Uruguay, Zambia, and Mexico.
