mineral

Quartz Geode

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: Clear to milky white; Luster: Vitreous/glassy; Crystal Structure: Hexagonal (trigonal); Cleavage: None/Conchoidal fracture; Specific gravity: 2.65

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

Identified April 14, 2026More mineral →

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Physical properties

Hardness: 7 (Mohs scale); Color: Clear to milky white; Luster: Vitreous/glassy; Crystal Structure: Hexagonal (trigonal); Cleavage: None/Conchoidal fracture; Specific gravity: 2.65

Formation & geological history

Formed as hollow cavities in volcanic or sedimentary rocks (often vesicles in lava or nodules in limestone) where mineral-rich groundwater precipitates quartz crystals over thousands of years.

Uses & applications

Commonly used for ornamental purposes, home decor, geological education, and mineral collecting.

Geological facts

Geodes are often referred to as 'thunder eggs' in some regions; they are essentially encapsulated crystal caves that look like boring rocks on the outside until cracked open.

Field identification & locations

Identify in the field by looking for rounded, lumpy nodules with a distinct lightweight feel compared to solid rocks of the same size. Large concentrations are found in Morocco, Brazil, and the USA (Iowa, Indiana).