mineral

Quartz Geode

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Clear to white (milky); Luster: Vitreous (glassy); Crystal Structure: Hexagonal; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Clear to white (milky)
Luster: Vitreous (glassy)

Identified June 24, 2026More mineral →

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Physical properties

Hardness: 7 on Mohs scale; Color: Clear to white (milky); Luster: Vitreous (glassy); Crystal Structure: Hexagonal; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed as secondary mineral precipitates in hollow cavities (vugs) within volcanic or sedimentary rocks. Over millions of years, silica-rich groundwater seeps into these cavities and slowly crystallizes.

Uses & applications

Primary use as ornamental display pieces, home decor, and in the lapidary arts. Quartz itself is vital for electronics (oscillators) and glassmaking.

Geological facts

Geodes are often referred to as 'thunder eggs' when they are solid or nearly solid. The name 'geode' comes from the Greek word 'Geoides' which means 'earth-like'.

Field identification & locations

Identified by a bumpy, non-descript exterior resembling a common rock that, when broken or cut, reveals a hollow interior lined with crystals. Commonly found in Brazil, Mexico, and the Midwestern USA (Indiana and Iowa).