sedimentary
Geode (unopened nodule)
Silicon Dioxide (SiO2) Nodule
Hardness: 7 (exterior), Color: Off-white to tan exterior, Luster: Dull/earthy exterior, Crystal structure: Trigonal (internal), specific gravity: 2.6-2.7
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Physical properties
Hardness: 7 (exterior), Color: Off-white to tan exterior, Luster: Dull/earthy exterior, Crystal structure: Trigonal (internal), specific gravity: 2.6-2.7
Formation & geological history
Formed in volcanic ash beds or sedimentary limestone voids where mineral-rich water precipitates silica over millions of years (Cenozoic to Paleozoic eras).
Uses & applications
Primarily used as collector specimens, educational items, and ornamental decoration once cut or cracked open.
Geological facts
The word geode comes from the Greek word 'Geoides' meaning earth-like. They look like ordinary rocks until opened to reveal crystals.
Field identification & locations
Identify by a rounded, bumpy 'cauliflower' texture and light weight compared to solid rocks. Commonly found in riverbeds or desert regions like the Keokuk area in the US.
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