sedimentary

Geode Nodules / Chalcedony Geode

Silicon Dioxide (SiO2) - Amorphous to Cryptocrystalline Quartz

AI-generated identification · may be incorrect

Hardness: 6.5–7 (Mohs scale); Color: Externally grey, brown, or tan; Luster: Dull/earthy on the exterior; Structure: Spherical or subspherical with a cauliflower-like texture; Specific Gravity: 2.6–2.7.

Hardness: 6
Color: Externally grey, brown, or tan
Luster: Dull/earthy on the exterior

Identified March 22, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the hollow filling of cavities in sedimentary or volcanic rock. Over millions of years, mineral-rich groundwater seeps into the cavity, depositing layers of silica that harden into chalcedony or quartz crystals.

Uses & applications

Primarily used for geological education, lapidary arts (cutting and polishing), jewelry (when sliced), and as decorative display pieces for collectors.

Geological facts

Geodes are essentially 'nature’s surprise packages.' Until they are cracked open, one can never be 100% sure if they are solid (nodules) or hollow with internal crystals. The largest geode ever found is the Empress of Uruguay, standing 11 feet tall.

Field identification & locations

Identify in the field by looking for rounded, lumpy, 'cauliflower-textured' rocks that feel unexpectedly light for their size (if hollow). Common in desert environments such as Morocco, Mexico, and the Midwestern USA (Keokuk region).