sedimentary
Geode (Unopened)
Chalcedony/Quartz Geode (SiO2)
Hardness: 7 (Mohs), Color: Tan to grey exterior (vuggy/bumpy texture), Luster: Dull/Earthy exterior, Crystal Structure: Hexagonal (inside), Specific Gravity: ~2.65
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Physical properties
Hardness: 7 (Mohs), Color: Tan to grey exterior (vuggy/bumpy texture), Luster: Dull/Earthy exterior, Crystal Structure: Hexagonal (inside), Specific Gravity: ~2.65
Formation & geological history
Formed in sedimentary rock cavities (typically limestone) via groundwater precipitation of minerals over millions of years, often in the Mississippian or Cenozoic periods.
Uses & applications
Collector specimens, decorative displays, lapidary use, and educational tools.
Geological facts
Geodes are often hollow, containing a 'rattle' sound if crystals have broken loose inside. The term 'geode' comes from the Greek word 'Geoides' meaning 'earth-like'.
Field identification & locations
Identified by their round or egg-like shape and cauliflower-like exterior texture. Commonly found in stream beds or limestone deposits in states like Iowa, Indiana, or Illinois in the US.
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