sedimentary
Quartz Geode with Chalcedony
Crystalline Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, and reddish-brown; Luster: Vitreous to waxy; Structure: Hexagonal/Trigonal; Cleavage: None; Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, and reddish-brown
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, and reddish-brown; Luster: Vitreous to waxy; Structure: Hexagonal/Trigonal; Cleavage: None; Specific Gravity: 2.65
Formation & geological history
Formed via chemical precipitation from mineral-rich groundwater filling cavities in sedimentary host rocks like limestone. As the water cools or evaporates, silica layers deposit along the walls, eventually forming crystals.
Uses & applications
Primarily used for ornamental decoration, gemstone collecting, holistic healing practices, and as education specimens.
Geological facts
Geodes are often hollow, but some fill completely to become nodules. The reddish-brown tint in this specimen is likely due to iron oxide impurities (Hematite or Goethite) present during formation.
Field identification & locations
Identified by the rounded exterior shell and inner crystalline cavity. Common in the Midwest United States (Keokuk region), Mexico, and Brazil. Check for high density and a hollow sound when tapped.
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