sedimentary

Geode (Unopened)

Chalcedony Geode (Hydrated Silicon Dioxide, SiO2)

AI-generated identification · may be incorrect

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

Identified June 25, 2026More sedimentary →

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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.