sedimentary

Geode (Quartz / Chalcedony Geode)

Silicon Dioxide (SiO2) - Quartz / Chalcedony

Hardness: 7 on Mohs scale (for the quartz lining). Color: Tan/brown earthy exterior with clear, white, or drusy quartz crystals inside. Luster: Vitreous to dull exterior, sparkling quartz interior. Cleavage: None.

Hardness: 7 on Mohs scale (for the quartz lining)
Luster: Vitreous to dull exterior, sparkling quartz interior

Identified July 27, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in volcanic rocks or sedimentary limestone beds when mineral-rich water precipitates crystals inside gas bubbles or hollow pockets over thousands to millions of years.

Uses & applications

Popular among collectors and educators; often cracked open, polished, or display specimens for home decor.

Geological facts

Geodes look like ordinary, rough rocks on the outside, but hiding inside are hollow cavities lined with brilliant mineral crystals. Iowa designated the geode as its official state rock in 1967.

Field identification & locations

Identified by its lightweight feel compared to solid rock of the same size, hollow sound when tapped, and round/sub-spherical shape. Commonly found in stream beds and limestone formations in places like Iowa, Missouri, Kentucky, Brazil, and Mexico.

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