Geode (unopened nodule)

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.

Identified on: 5/6/2026

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