sedimentary
Geode (Unopened)
Chalcedony Geode (Hydrated Silicon Dioxide, SiO2)
Hardness: 6.5-7 (shell); Color: Tan, brown, or gray exterior; Luster: Dull/earthy exterior; Crystal structure: Trigonal (internal nanocrystals); Specific gravity: 2.60-2.65
- Hardness
- 6
- Color
- Tan, brown, or gray exterior
- Luster
- Dull/earthy exterior
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Physical properties
Hardness: 6.5-7 (shell); Color: Tan, brown, or gray exterior; Luster: Dull/earthy exterior; Crystal structure: Trigonal (internal nanocrystals); Specific gravity: 2.60-2.65
Formation & geological history
Formed as hollow cavities in sedimentary or volcanic rock that are filled through precipitation from hydrothermal fluids or groundwater. These can date back millions of years depending on the host formation.
Uses & applications
Used primarily for geological collecting, home decor, lapidary arts, and educating students on mineral growth.
Geological facts
The word geode comes from the Greek word 'Geoides' meaning earth-like. They appear to be ordinary rocks on the outside but contain hollow centers filled with crystals like quartz, amethyst, or calcite.
Field identification & locations
Identify by their rounded, lumpy appearance and unusually light weight for their size. Commonly found in desert regions, riverbeds, and volcanic ash deposits in locations like Indiana, Iowa, or Mexico.
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