sedimentary

Geode (Quartz / Chalcedony Geode)

SiO2 (Silicon Dioxide)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale; Color: Tan/brown exterior with brownish-red/orange iron-stained interior; Luster: Earthy exterior, vitreous to dull interior; Crystal structure: Trigonal (microcrystalline/cryptocrystalline quartz); Cleavage: None.

Hardness: 6
Luster: Earthy exterior, vitreous to dull interior

Identified July 27, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed when mineral-rich water precipitates minerals within gas bubbles in volcanic rock or cavities in sedimentary rock layers over thousands to millions of years.

Uses & applications

Popular as decorative display specimens, educational samples, lapidary projects, and gemstone collecting.

Geological facts

Geodes appear to be ordinary, plain rocks on the outside, but cracking them open reveals hollow cavities lined with crystals. Iron oxide impurities often give the interior red, orange, or rusty yellow coloration.

Field identification & locations

Identified by a rounded, bumpy exterior shell combined with a lighter weight than solid rock of equivalent size due to the hollow interior cavity. Common in regions like the Midwestern US, Mexico, and Brazil.