mineral
Quartz Geode
Silicon Dioxide (SiO2) in a sedimentary or volcanic host
Hardness: 7 (Mohs scale); Color: White to translucent crystals with a gray/tan outer rind; Luster: Vitreous/glassy crystals; Crystal structure: Trigonal; Cleavage: None/Conchoidal fracture.
- Hardness
- 7 (Mohs scale)
- Color
- White to translucent crystals with a gray/tan outer rind
- Luster
- Vitreous/glassy crystals
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Physical properties
Hardness: 7 (Mohs scale); Color: White to translucent crystals with a gray/tan outer rind; Luster: Vitreous/glassy crystals; Crystal structure: Trigonal; Cleavage: None/Conchoidal fracture.
Formation & geological history
Formed when gas bubbles in volcanic rock or hollow cavities in sedimentary rock are filled by slow mineral precipitation from hydrothermal fluids or groundwater. These can take millions of years to form.
Uses & applications
Predominantly used for home decor, educational specimens, metaphysical collecting, and jewelry lapidary work.
Geological facts
Geodes are essentially 'petrified bubbles.' While they look like ordinary rocks on the outside, their hollow interiors can contain a variety of minerals, including quartz, amethyst, or calcite.
Field identification & locations
Identify in the field by looking for rounded, lumpy nodules that feel lighter than they look (indicating a hollow center). Common locations include the Midwest USA (Keokuk), Brazil, and Mexico.
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