sedimentary

Quartz Geode

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: Gray/white translucent crystals inside a tan/brown exterior shell; Luster: Vitreous (glassy) crystals with a dull, earthy rind; Crystal structure: Hexagonal/trigonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 (Mohs scale)
Luster: Vitreous (glassy) crystals with a dull, earthy rind

Identified March 30, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the precipitation of minerals from hydrothermal fluids or groundwater into hollow cavities within sedimentary or volcanic rock. These cavities are often gas bubbles (vesicles) or spaces left by decayed organic matter. They can date back millions of years depending on the host rock formation.

Uses & applications

Hobbyist collecting, educational use in geology labs, ornamental decoration, and small-scale jewelry components (slices).

Geological facts

Geodes are essentially 'petrified bubbles'. While the exterior looks like a common rock, the interior is hollow and lined with crystals. The word 'geode' comes from the Greek word 'Geoides' meaning 'earth-like'.

Field identification & locations

Identify in the field by looking for rounded, cauliflower-like exterior textures that feel abnormally light for their size. Commonly found in desert regions, volcanic ash beds, or limestone regions such as those in Iowa, Missouri, and Mexico. Collectors should look for 'rattlers' - geodes with loose crystals inside.