sedimentary
Quartz Geode
Quartz (Silicon Dioxide, SiO2) Geode
Hardness: 7 (Mohs scale); Color: Grayish-white to clear interior, dark green to gray rind; Luster: Vitreous/Glassy; Structure: Hexagonal crystals; Cleavage: None (conchoidal fracture).
- Hardness
- 7 (Mohs scale)
- Color
- Grayish-white to clear interior, dark green to gray rind
- Luster
- Vitreous/Glassy
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Physical properties
Hardness: 7 (Mohs scale); Color: Grayish-white to clear interior, dark green to gray rind; Luster: Vitreous/Glassy; Structure: Hexagonal crystals; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed as secondary fillings in hollow cavities within sedimentary rocks or volcanic ash. Silica-rich groundwater precipitates crystals over millions of years. This specimen appears typical of those found in limestone formations.
Uses & applications
Aesthetic decoration, lapidary arts, metaphysical use, and as a popular educational specimen for mineral collectors.
Geological facts
Geodes are often referred to as 'thunder eggs' when filled solid. While they appear like ordinary rocks on the exterior, they contain hollow cavities lined with inward-growing crystals.
Field identification & locations
Identify in the field by their rounded, bumpy exterior and unusual lightness for their size. This specific specimen shows a 'druzy' quartz layer on a darker chalcedony/limestone base. Commonly found in Morocco or the American Midwest.
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