mineral

Quartz geode

Microcrystalline and crystalline quartz (SiO₂), likely chalcedony-lined geode

AI-generated identification · may be incorrect

White to translucent quartz/chalcedony with a druzy crystal cavity and brown, iron-oxide-stained outer rind; vitreous to waxy luster, Mohs hardness 7 for quartz (about 6.5–7 for chalcedony), conchoidal fracture, no cleavage, hexagonal quartz crystals. Specific gravity is approximately 2.6.

Identified August 9, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills vesicles or cavities in volcanic rock, depositing chalcedony and later quartz crystals in layers. Such geodes commonly formed in volcanic rocks during the Cenozoic or older, depending on locality.

Uses & applications

Used as decorative specimens, bookends, carvings, and lapidary material; attractive crystal-lined pieces may be collected or sold as display minerals.

Geological facts

The hollow interior records repeated episodes of mineral precipitation, and the brown exterior commonly reflects oxidation of iron-bearing minerals.

Field identification & locations

Look for a rounded, weathered rind and a hollow or partly filled interior lined with tiny quartz crystals; quartz will scratch glass, but testing should be done inconspicuously. Common sources include Brazil, Uruguay, Mexico, and the U.S. Midwest.