mineral
Amethyst
Silicon dioxide (SiO2) with iron impurities
Hardness: 7 on Mohs scale; Color: Purple to violet; Luster: Vitreous (glassy); Crystal structure: Hexagonal (trigonal); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Purple to violet
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 7 on Mohs scale; Color: Purple to violet; Luster: Vitreous (glassy); Crystal structure: Hexagonal (trigonal); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Forms in hydrothermal veins and volcanic cavities (geodes). The purple color is caused by gamma irradiation of iron impurities within the quartz structure. Most specimens range from late Mesozoic to Cenozoic eras.
Uses & applications
Primary use in jewelry, gemstone collecting, and ornamental carvings. Historically used in drinking vessels to prevent intoxication.
Geological facts
Amethyst is the birthstone for February. Large geodes are frequently found in Brazil and Uruguay. The name comes from the Ancient Greek 'amethystos', meaning 'not intoxicated'.
Field identification & locations
Identify by its distinct purple color and crystal habit. Often found in basalt vugs. Collectors look for deep 'Siberian' purple with red and blue flashes. Can be found in many gravel pits or volcanic regions.
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