sedimentary
Quartz Geode
Silicon dioxide (SiO2)
Hardness of 7 on the Mohs scale, typically grayish-brown exterior with a crystalline quartz interior, vitreous luster, trigonal crystal system, no cleavage, specific gravity of 2.65.
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Physical properties
Hardness of 7 on the Mohs scale, typically grayish-brown exterior with a crystalline quartz interior, vitreous luster, trigonal crystal system, no cleavage, specific gravity of 2.65.
Formation & geological history
Formed in cavities in sedimentary or volcanic rocks where groundwater rich in dissolved silica precipitates crystals over millions of years.
Uses & applications
Used in mineral collecting, decorative display pieces, and sometimes lapidary work.
Geological facts
Geodes start as hollow bubbles in rock, often formed by animal burrows, tree roots, or gas bubbles in volcanic rock, which slowly fill with mineral-rich water.
Field identification & locations
Found worldwide in limestone formations and volcanic regions; easily identified by their weathered, bumpy exterior and glittering crystalline hollow core.
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