mineral

Quartz Geode

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale), Color: Clear to milky white, Luster: Vitreous/glassy, Crystal structure: Trigonal (hexagonal prisms), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65

Identified April 20, 2026More mineral →

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Physical properties

Hardness: 7 (Mohs scale), Color: Clear to milky white, Luster: Vitreous/glassy, Crystal structure: Trigonal (hexagonal prisms), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65

Formation & geological history

Formed in cavities within volcanic or sedimentary rocks. As mineral-rich water seeps into these hollow spaces, silica precipitates and slowly grows crystals pointing inward over thousands of years.

Uses & applications

Primarily used as decorative display pieces, for educational purposes in geology, and by crystal collectors. Smaller clear crystals may be used in jewelry.

Geological facts

Geodes are often referred to as 'thunder eggs' in some regions. While they look like ordinary rocks on the outside, their hollow interiors can contain a variety of minerals besides quartz, such as amethyst, calcite, or celestite.

Field identification & locations

Identify in the field by looking for rounded, bumpy, potato-like rocks that feel lighter than they look (indicating a hollow center). Common locations include the American Midwest, Brazil, Morocco, and Mexico.