mineral

Geode (Quartz)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Clear to white/milky interior with a brown or gray stony exterior; Luster: Vitreous (glassy) crystals; Crystal Structure: Hexagonal (trigonal); Cleavage: None/Conchoidal fracture; Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Luster: Vitreous (glassy) crystals

Identified March 1, 2026More mineral →

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Physical properties

Formation & geological history

Formed in volcanic or sedimentary rock cavities. Over millions of years, mineral-rich water seeps into hollow pockets (often gas bubbles in lava or animal burrows in mud), depositing layers of silica that crystallize as quartz.

Uses & applications

Primary uses include home decor, jewelry, metaphysical collecting, and geological education. High-quality quartz is also used in electronics for its piezoelectric properties.

Geological facts

Geodes are often referred to as 'thunder eggs' in some regions. While they look like ordinary rocks on the outside, their hollow centers can contain rare varieties of quartz such as amethyst, citrine, or even secondary minerals like calcite or celestite.

Field identification & locations

Identify in the field by looking for round, bumpy, 'cauliflower-like' exterior textures; they usually feel lighter than solid rocks of the same size. Commonly found in deserts, volcanic ash beds, or limestone regions like Brazil, Mexico, and the Midwestern USA.