mineral
Quartz Geode
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale. Color: White to transparent, sometimes with yellowish or brownish tinges. Luster: Vitreous (glassy). Crystal structure: Trigonal. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 7 on Mohs scale. Color: White to transparent, sometimes with yellowish or brownish tinges. Luster: Vitreous (glassy). Crystal structure: Trigonal. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
Formation & geological history
Formed in hollow cavities in rocks, most commonly in sedimentary limestone or volcanic basalt, through the slow precipitation of silica-rich groundwater over millions of years.
Uses & applications
Used in decorative items, lapidary art, crystal collections, and sometimes in electronic applications or glass-making depending on purity.
Geological facts
Geodes start as gas bubbles in volcanic rock or animal burrows/nodules in sedimentary layers. Over time, mineral-rich water seeps in and deposits crystals layer by layer, growing inward from the outer wall toward the center.
Field identification & locations
Easily identified by its rough outer rock shell enclosing a hollow cavity lined with sparkling quartz crystal points. Found worldwide, particularly in locations like Brazil, Mexico, and the USA (e.g., Keokuk, Iowa).
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