mineral
Amethyst and Agate Geode Section
Silicon Dioxide (SiO2) - Crystalline Quartz and Chalcedony
Hardness: 7 (Mohs); Color: Purple to violet crystalline quartz with translucent gray/white banded agate; Luster: Vitreous to waxy; Crystal Structure: Hexagonal (trigonal); Specific Gravity: 2.65
- Hardness
- 7 (Mohs)
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 (Mohs); Color: Purple to violet crystalline quartz with translucent gray/white banded agate; Luster: Vitreous to waxy; Crystal Structure: Hexagonal (trigonal); Specific Gravity: 2.65
Formation & geological history
Formed in volcanic or sedimentary cavities (vugs) where silica-rich fluids deposited layers of chalcedony followed by large quartz crystals. Most large amethyst deposits are Cretaceous in age.
Uses & applications
Used primarily in lapidary work, jewelry making, and as ornamental display pieces in crystal collections.
Geological facts
The purple color is caused by iron impurities irradiated by natural radiation from surrounding rock. This specimen shows a mix of microcrystalline agate banding and macrocrystalline amethyst points.
Field identification & locations
Identify by purple crystal points and conchoidal fracture. Often found within basalt host rock. Major deposits are in Brazil, Uruguay, and Morocco.
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