mineral
Quartz geode (likely chalcedony-lined geode)
Silica geode: microcrystalline quartz/chalcedony with drusy quartz (SiO₂), possibly iron-oxide staining
AI-generated identification · may be incorrectHardness 6.5–7 Mohs; white to translucent gray quartz crystals with cream-orange, iron-stained chalcedony and earthy matrix. Vitreous to waxy luster, trigonal quartz structure, conchoidal fracture, and no obvious cleavage; typical specific gravity is about 2.65.
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Physical properties
Hardness 6.5–7 Mohs; white to translucent gray quartz crystals with cream-orange, iron-stained chalcedony and earthy matrix. Vitreous to waxy luster, trigonal quartz structure, conchoidal fracture, and no obvious cleavage; typical specific gravity is about 2.65.
Formation & geological history
Forms when silica-rich groundwater fills cavities in volcanic rock or sedimentary concretions, depositing chalcedony first and quartz crystals later. Individual geodes commonly formed during Cenozoic to older volcanic or sedimentary episodes, depending on locality.
Uses & applications
Used as a decorative specimen, paperweight, and lapidary material; attractive crystal-lined cavities have modest collector value. It is not generally used as construction stone.
Geological facts
The hollow cavity and crystal lining are diagnostic of a geode; orange coloration is commonly goethite or hematite staining rather than orange quartz. The outer rind appears weathered and iron-rich.
Field identification & locations
Identify by a hard, silica-rich rind surrounding an open cavity lined with sparkly quartz or chalcedony; common sources include Brazil, Uruguay, Mexico, Morocco, and the western United States. A steel file should not easily scratch quartz.
