mineral

Botryoidal chalcedony geode

Microcrystalline quartz (SiO₂), likely chalcedony with quartz druse

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent gray, cream, and brown with a waxy chalcedony exterior and sparkly vitreous quartz crystals inside. It has no cleavage, conchoidal fracture, and a typical specific gravity near 2.6.

Identified September 20, 2026More mineral →

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Physical properties

Formation & geological history

Silica-rich groundwater filled a cavity in volcanic rock, depositing chalcedony and later quartz crystals, commonly during Cenozoic volcanic activity. The brown outer coloration is likely iron staining or host-rock residue.

Uses & applications

Used as a decorative specimen, lapidary material, and occasionally in jewelry; small common pieces have modest commercial value.

Geological facts

The inner crystal lining is called druse or druzy quartz. Chalcedony forms from very fine quartz fibers, producing its characteristic smooth, waxy appearance.

Field identification & locations

Identify it by the hard, translucent silica rind and tiny sparkling quartz crystals lining a cavity; it will scratch glass but not be scratched by a steel knife. Common sources include volcanic regions of Brazil, Uruguay, Mexico, the western United States, and Turkey.