Quartz Geode

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).

Identified on: 4/14/2026

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