sedimentary
Quartz Geode
Silicon Dioxide (SiO2) in Geodic Cavity
Hardness: 7 (Mohs scale); Color: White to translucent; Luster: Vitreous/glassy on internal crystals, dull on outer rind; Crystal Structure: Trigonal/Hexagonal; Cleavage: None/Conchoidal fracture.
- Hardness
- 7 (Mohs scale)
- Color
- White to translucent
- Luster
- Vitreous/glassy on internal crystals, dull on outer rind
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Physical properties
Hardness: 7 (Mohs scale); Color: White to translucent; Luster: Vitreous/glassy on internal crystals, dull on outer rind; Crystal Structure: Trigonal/Hexagonal; Cleavage: None/Conchoidal fracture.
Formation & geological history
Formed as secondary mineral deposits in hollow cavities of sedimentary or volcanic rocks. Mineral-rich groundwater seeps into these cavities, slowly precipitating crystals over millions of years.
Uses & applications
Primarily used as decorative display specimens, educational tools in geology, and for lapidary work. Small, clear crystals are sometimes used in jewelry.
Geological facts
The word geode comes from the Greek word 'Geoides' which means earth-like. Unlike vugs, geodes can often be separated from the surrounding host rock as intact nodules or spheres.
Field identification & locations
Identify by the rough, cauliflower-like outer texture and the hollow, crystal-lined interior. Common in regions like the midwestern United States (e.g., Keokuk, Iowa), Morocco, and Brazil.
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