sedimentary
Quartz Geode
Silicon Dioxide (SiO2) in a Sedimentary Vug
Hardness: 7 (Mohs), Color: White to translucent crystals with a tan/brown exterior, Luster: Vitreous (glassy) inside to dull outside, Crystal Structure: Hexagonal (trigonal), Cleavage: None (conchoidal fracture)
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Physical properties
Hardness: 7 (Mohs), Color: White to translucent crystals with a tan/brown exterior, Luster: Vitreous (glassy) inside to dull outside, Crystal Structure: Hexagonal (trigonal), Cleavage: None (conchoidal fracture)
Formation & geological history
Formed by the precipitation of mineral-rich water within a hollow cavity or gas bubble in sedimentary rock or volcanic ash, often occurring over thousands of years. Usually found in limestone or shale beds.
Uses & applications
Decorative display pieces, lapidary use, educational specimens, and metaphysical collecting.
Geological facts
Geodes are essentially 'rock eggs' that appear ordinary on the outside but contain hollow centers lined with crystals. Many in the US are found in the Keokuk region of Iowa, Illinois, and Missouri.
Field identification & locations
Identify by looking for rounded, lumpy nodules that feel lighter than they look (indicating a hollow center). In the field, look for 'cauliflower' textured exteriors in stream beds or limestone outcrops.
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