mineral
Botryoidal Chalcedony (Agate)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: translucent gray/white, Luster: waxy to vitreous, Crystal Structure: Trigonal (microcrystalline/cryptocrystalline), Cleavage: None, Specific Gravity: 2.58-2.64
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: translucent gray/white, Luster: waxy to vitreous, Crystal Structure: Trigonal (microcrystalline/cryptocrystalline), Cleavage: None, Specific Gravity: 2.58-2.64
Formation & geological history
Formed from the deposition of silica-rich water in cavities (vugs) or fractures of igneous or sedimentary rocks. The 'botryoidal' (grape-like) texture forms as the mineral grows outward from multiple centers.
Uses & applications
Used primarily for lapidary work, jewelry, and mineral collecting. Large-scale chalcedony is used in industrial abrasives and precision bearings.
Geological facts
Chalcedony was highly prized in the ancient world for making seals and amulets. The term 'botryoidal' comes from the Greek word 'botrys', meaning a bunch of grapes.
Field identification & locations
Identify in the field by its bubbly, rounded surface and waxy luster. It will scratch glass but cannot be scratched by a steel knife. Common in volcanic regions and desert silicate deposits.
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