mineral
Amethyst Geode
Quartz (SiO2, variety Amethyst)
Hardness of 7 on the Mohs scale; purple to violet color caused by iron impurities and irradiation; vitreous luster; hexagonal crystal system; conchoidal fracture with no true cleavage; specific gravity of 2.65.
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Physical properties
Hardness of 7 on the Mohs scale; purple to violet color caused by iron impurities and irradiation; vitreous luster; hexagonal crystal system; conchoidal fracture with no true cleavage; specific gravity of 2.65.
Formation & geological history
Formed within gas cavities in volcanic rocks (vesicles in basalt or andesite) where silica-rich hydrothermal fluids slowly cool and deposit microcrystalline quartz followed by macrocrystalline quartz crystals pointing inward.
Uses & applications
Widely used in jewelry, ornamental carvings, crystal healing, home decor, and as popular specimens for mineral collectors.
Geological facts
Amethyst was once considered one of the cardinal gemstones alongside diamond, ruby, emerald, and sapphire until large deposits were discovered in Brazil. Its purple color fades if left in direct sunlight for extended periods.
Field identification & locations
Easily identifiable in the field or home by its characteristic purple quartz crystal points lining a rounded cavity with a basalt or agate outer rind. Major sources include Brazil, Uruguay, and parts of the United States.
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