sedimentary
Geode
Quartz nodule / Chalcedony-lined cavity
AI-generated identification · may be incorrectHardness of 7 on the Mohs scale (for the quartz interior), varies in color from white, grey, brown to translucent, dull outer crust with vitreous or sparkly interior crystals, cryptocrystalline to microcrystalline structure, no distinct cleavage.
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Physical properties
Hardness of 7 on the Mohs scale (for the quartz interior), varies in color from white, grey, brown to translucent, dull outer crust with vitreous or sparkly interior crystals, cryptocrystalline to microcrystalline structure, no distinct cleavage.
Formation & geological history
Formed in sedimentary or volcanic rocks where groundwater dissolves cavity minerals and deposits silica over millions of years.
Uses & applications
Commonly collected as lapidary specimens, used in decorative items and jewelry making.
Geological facts
Geodes often start as hollow bubbles in volcanic rock or animal burrows in sedimentary rock, gradually filling with mineral-rich water.
Field identification & locations
Found worldwide in limestone formations, volcanic ash beds, and deserts; often identified by their rounded, knobby exterior and hollow, crystal-lined interior when cracked open.
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