mineral

Quartz geode fragment

Microcrystalline quartz (chalcedony) with drusy quartz; SiO₂

AI-generated identification · may be incorrect

White to gray, rough outer chalcedony rind with a small hollow lined by sparkling quartz crystals; vitreous to waxy luster, Mohs hardness about 7, no cleavage, conchoidal fracture, and specific gravity near 2.6. The specimen appears naturally broken rather than polished.

Identified September 22, 2026More mineral →

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Physical properties

Formation & geological history

Formed when silica-rich groundwater filled a gas cavity or vesicle in volcanic rock, depositing chalcedony first and quartz crystals later. Such geodes commonly formed in volcanic rocks during the Cenozoic or older episodes, depending on locality.

Uses & applications

Small pieces are used as inexpensive mineral specimens, educational samples, décor, and occasionally in jewelry or lapidary work. This fragment has modest collector value.

Geological facts

The hollow center records changing fluid chemistry during growth: fine chalcedony commonly formed before the larger inner quartz crystals. Colorless or gray drusy quartz is among the most widespread geode interiors.

Field identification & locations

Identify it by the hard white-gray rind and crystalline cavity; a steel file should not easily scratch the quartz. Common sources include Brazil, Uruguay, Mexico, Morocco, and the United States, especially Indiana and Iowa.