mineral

Quartz Geode

Silicon Dioxide (SiO2) in Geode form

Hardness: 7 Mohs scale; Color: Clear to milky white crystals with gray/tan outer rind; Luster: Vitreous (glassy) for crystals, earthy for rind; Crystal Structure: Hexagonal; Cleavage: None/Conchoidal fracture; Specific Gravity: 2.65

Hardness: 7 Mohs scale
Color: Clear to milky white crystals with gray/tan outer rind
Luster: Vitreous (glassy) for crystals, earthy for rind

Identified July 15, 2026More mineral →

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Physical properties

Formation & geological history

Formed as secondary mineral precipitation within cavities of volcanic or sedimentary rocks. Silica-rich water seeps into voids (gas bubbles in lava or burrows in sedimentary layers), slowly growing crystals inward over millions of years.

Uses & applications

Primarily used for high-end decor, metaphysical collecting, educational specimens, and amateur lapidary work.

Geological facts

Geodes are often referred to as 'thunder eggs' when they are completely filled (nodules). Small geodes like this one are common in the Midwest United States, particularly the Keokuk region.

Field identification & locations

Identify in the field by looking for rounded, hollow-feeling rocks with a bumpy, cauliflower-like exterior texture. They are significantly lighter than solid rocks of the same size.