sedimentary

Geode

Silicon dioxide (Quartz/Chalcedony) in carbonate/volcanic host rock

AI-generated identification · may be incorrect

Mohs hardness 7 for the quartz crystals inside. Color varies from clear to purple, brown, or white. Vitreous to dull luster with a cryptocrystalline or macrocrystalline structure.

Identified November 11, 2026More sedimentary →

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Physical properties

Mohs hardness 7 for the quartz crystals inside. Color varies from clear to purple, brown, or white. Vitreous to dull luster with a cryptocrystalline or macrocrystalline structure.

Formation & geological history

Formed when mineral-rich groundwater deposits silica inside gas cavities in volcanic or sedimentary rock over millions of years.

Uses & applications

Used primarily in lapidary arts, jewelry making, and as decorative display specimens for rock collectors.

Geological facts

Geodes often feature sparkling quartz or amethyst crystal interiors completely hidden beneath a drab, bumpy outer shell. They form strictly within hollow cavities or vesicles of host rock.

Field identification & locations

Identify in the field by looking for spherical, bumpy, lighter-weight nodular rocks that sound hollow when gently tapped. Commonly found in limestone formations and volcanic ash beds worldwide.