mineral
Geode (Unopened)
Quartz Geode (SiO2) / Chalcedony Concretion
Hardness: 7 on Mohs scale; Color: Beige, tan, grey, to brownish exterior; Luster: Dull, earthy exterior, glassy/vitreous interior crystals; Structure: Spherical to subspherical hollow nodule
- Hardness
- 7 on Mohs scale
- Color
- Beige, tan, grey, to brownish exterior
- Luster
- Dull, earthy exterior, glassy/vitreous interior crystals
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Physical properties
Hardness: 7 on Mohs scale; Color: Beige, tan, grey, to brownish exterior; Luster: Dull, earthy exterior, glassy/vitreous interior crystals; Structure: Spherical to subspherical hollow nodule
Formation & geological history
Formed in sedimentary rock beds (limestone or dolomite) or volcanic ash deposits where groundwater mineral solutions (silica/calcium carbonate) gradually precipitate inward inside hollow cavities over millions of years.
Uses & applications
Popular for rockhounding, lapidary cutting, cracking open to reveal crystal interior, educational specimens, and display decor.
Geological facts
Unopened geodes are often called 'rattlers' if the crystals inside have broken loose and make noise when shaken. The rough bumpy exterior is typically made of chalcedony or weathered limestone/chert.
Field identification & locations
Identified by its rough, cauliflowered or bumpy, rounded exterior shape and lighter relative weight compared to a solid rock of the same size. Commonly found in locations like Keokuk (Iowa, Missouri, Illinois), Indiana, Kentucky, Brazil, and Mexico.
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