sedimentary

Geode Nodules / Keokuk Geode

Quartz / Chalcedony Geode (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5 - 7 on the Mohs scale. Color: Greyish-tan, greenish, brownish exterior with quartz crust. Luster: Dull or earthy exterior, vitreous inside. Structure: Round to subspherical, rough and bumpy knobby texture.

Hardness: 6
Color: Greyish-tan, greenish, brownish exterior with quartz crust
Luster: Dull or earthy exterior, vitreous inside

Identified July 25, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed as secondary structures within sedimentary rock (limestone or shale) or volcanic cavities. Mineral-rich groundwater precipitates quartz, chalcedony, or calcite layer by layer inside hollow cavities over millions of years.

Uses & applications

Lapidary work, gemstone cutting, mineral collecting, education, decorative display pieces.

Geological facts

Unbroken geode nodules feel surprisingly light for their size if they are hollow inside containing crystal cavities. The State of Iowa named the Keokuk geode as its official state rock in 1967.

Field identification & locations

Look for rounded, cauliflower-like, or bumpy sphere-like stones that feel unusually lightweight compared to solid rocks of similar size. Common in limestone outcrops along stream beds in the Midwestern United States (Iowa, Illinois, Missouri) and desert regions worldwide.