sedimentary
Quartz Geode
Silicon Dioxide (SiO2) in Host Rock
Hardness: 7 (Mohs scale), Color: White to colorless crystals with tan/pink host rock, Luster: Vitreous (glassy) to dull, Crystal Structure: Hexagonal, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: White to colorless crystals with tan/pink host rock, Luster: Vitreous (glassy) to dull, Crystal Structure: Hexagonal, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed in sedimentary or volcanic rock cavities. Mineral-rich water seeps into hollow pockets, precipitating crystals over millions of years. This host material appears to be a rhyolitic or sedimentary matrix.
Uses & applications
Commonly used for geological education, home decor, lapidary projects, and as a popular item for novice collectors.
Geological facts
Geodes are often referred to as 'thunder eggs' when they are solid or have specific patterns. The word 'geode' comes from the Greek word 'geodes' meaning earth-like.
Field identification & locations
Identify in the field by looking for rounded, lumpy nodules that feel lighter than solid rocks of similar size. Common in areas like the American Southwest, Mexico, and Brazil.
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