sedimentary

Geode (Unopened) / Quartz Nodule

Silicon Dioxide (SiO2) within a sedimentary/volcanic nodule

AI-generated identification · may be incorrect

Hardness: typically 6.5 - 7 on the Mohs scale for the quartz/chalcedony shell; Color: exterior is tan, beige, brown, and reddish-orange from iron oxide staining; Luster: earthy and dull on the crust, vitreous or waxy if fractured inside; Specific Gravity: ~2.6 - 2.65

Hardness: typically 6

Identified October 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed either by the filling of gas bubbles in volcanic rocks or cavities left by dissolved minerals/fossils in sedimentary limestone/shale. Mineral-rich groundwater precipitates chalcedony and quartz inward layer by layer.

Uses & applications

Lapidary arts, mineral collecting, education, cracking or cutting open to display internal crystals.

Geological facts

Geodes often feel surprisingly light for their size if they contain a hollow, crystal-lined center. The reddish-orange coloration on the exterior is usually due to secondary iron oxide (limonite or hematite) deposits.

Field identification & locations

Identified by its rounded to sub-rounded nodular shape, lumpy 'cauliflower' or weathered exterior rind, and relatively low density compared to solid rocks of similar size. Commonly found in regions like Keokuk (Iowa/Illinois/Missouri), Chihuahua (Mexico), and Morocco.