Mineral/Sedimentary

Quartz Geode

Silicon Dioxide (SiO2)

Hardness: 7.0 on Mohs scale; Color: Clear to milky white crystals; Luster: Vitreous (glassy); Crystal Structure: Hexagonal (trigonal); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7
Color: Clear to milky white crystals
Luster: Vitreous (glassy)

Identified March 5, 2026More mineral/sedimentary →

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Physical properties

Hardness: 7.0 on Mohs scale; Color: Clear to milky white crystals; Luster: Vitreous (glassy); Crystal Structure: Hexagonal (trigonal); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed in hollow cavities of sedimentary or volcanic rock. Over millions of years (often during the Cretaceous period), mineral-rich groundwater seeps into the cavity, depositing microscopic layers of silica which eventually grow into larger crystals.

Uses & applications

Used primarily as decorative ornaments, educational specimens for geology, and in 'metaphysical' collections. Industrial quartz is used in glassmaking and electronics, but geodes specifically are collector items.

Geological facts

Geodes are often called 'thunder eggs' when they are completely filled with solid minerals. The word 'geode' comes from the Greek word 'Geoides' which means 'earth-like'.

Field identification & locations

Identify in the field by looking for rounded, lumpy, cauliflower-like nodules that are lighter than solid rocks of similar size. Common locations include Morocco, Brazil, and the Midwestern United States (Iowa/Illinois border).