mineral
Quartz Geode (Chalcedony)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Creamy white to light tan; Luster: Waxy to vitreous; Crystal structure: Hexagonal (Trigonal); Cleavage: None; SG: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Creamy white to light tan
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Creamy white to light tan; Luster: Waxy to vitreous; Crystal structure: Hexagonal (Trigonal); Cleavage: None; SG: 2.65
Formation & geological history
Formed in cavities within sedimentary or volcanic rocks by mineral-rich water precipitation. Silica-rich fluids seep into voids, slowly crystallizing over thousands of years.
Uses & applications
Primarily used as decorative display specimens, for lapidary work (slicing and polishing), and in crystal collecting.
Geological facts
This specimen shows botryoidal (grape-like) chalcedony and a central vug or cavity. Geodes are essentially time capsules of geological activity from millions of years ago.
Field identification & locations
Identify by its bumpy, nodular exterior and hollow interior. Common in limestone regions or volcanic ash beds. Look for unusually light weight for its size, indicating a hollow center.
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