sedimentary
Quartz Geode
Silicon Dioxide (SiO2)
Mohs hardness of 7, white or clear crystalline appearance, vitreous to sugary luster, trigonal crystal system, conchoidal fracture with no true cleavage, specific gravity of 2.65
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Physical properties
Mohs hardness of 7, white or clear crystalline appearance, vitreous to sugary luster, trigonal crystal system, conchoidal fracture with no true cleavage, specific gravity of 2.65
Formation & geological history
Formed in cavities of sedimentary or volcanic rocks where silica-rich groundwater percolates and slowly precipitates quartz crystals over millions of years.
Uses & applications
Used in decorative display, crystal collecting, mineral specimens, and occasionally lapidary work.
Geological facts
Geodes appear as ordinary, unassuming spherical rocks on the outside, but cracking them open reveals a sparkling hollow interior lined with crystal formations.
Field identification & locations
Found worldwide, notably in regions with limestone deposits or volcanic ash beds such as Mexico, Brazil, and the Midwestern United States (e.g., Keokuk, Iowa).
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