mineral

Quartz Geode

Silicon Dioxide (SiO2) in a Secondary Sedimentary/Volcanic cavity

Hardness: 7 (Mohs scale), Color: Clear/White crystals with a brown/grey outer rind, Luster: Vitreous to greasy, Crystal structure: Trigonal (hexagonal prisms), Cleavage: None (conchoidal fracture), Specific gravity: 2.65

Identified March 12, 2026More mineral →

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Physical properties

Formation & geological history

Formed as secondary mineral precipitates within gas bubbles in volcanic rocks or hollow cavities in sedimentary limestone. Over millions of years, silica-rich groundwater seeps into these cavities, depositing layers of chalcedony and macro-crystalline quartz.

Uses & applications

Primarily used for decorative purposes, crystal healing, educational specimens, and small-scale jewelry (lapidary art). High-purity quartz from geodes can theoretically be used in glassmaking or electronics, though bulk sources are preferred.

Geological facts

The word 'geode' comes from the Greek 'geoides,' meaning 'earth-like.' While they look like ordinary rocks on the outside, they are often hollow and contain beautiful internal crystal 'gardens' that have remained sealed for millions of years.

Field identification & locations

Identify in the field by looking for a bumpy, cauliflower-like exterior texture and a rock that feels surprisingly light for its size (indicating a hollow center). Common locations include the Keokuk region (Iowa, USA), Mexico, and Brazil. Collectors look for unbroken nodules to crack open themselves.

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