mineral
Quartz geode slice
Microcrystalline and crystalline quartz, silicon dioxide (SiO₂)
AI-generated identification · may be incorrectWhite to translucent drusy quartz lining a rounded cavity, with a dull gray-brown outer rind; vitreous luster, hexagonal crystal structure, Mohs hardness 7, no cleavage, and specific gravity about 2.65.
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Physical properties
White to translucent drusy quartz lining a rounded cavity, with a dull gray-brown outer rind; vitreous luster, hexagonal crystal structure, Mohs hardness 7, no cleavage, and specific gravity about 2.65.
Formation & geological history
Formed when silica-rich groundwater filled a vesicle or cavity in volcanic rock, depositing chalcedony and later quartz crystals. The exact age is unknown; similar geodes commonly form in Cenozoic volcanic rocks.
Uses & applications
Used as a decorative specimen, paperweight, and lapidary material; attractive crystal-lined pieces may be mounted or polished for display.
Geological facts
The rough outer shell is commonly chalcedony or silica-rich volcanic material, while the sparkling interior consists of quartz crystals. The specimen appears cut or broken open rather than naturally exposed.
Field identification & locations
Identify quartz by its glassy sparkle, hardness, lack of cleavage, and inability to scratch it with a steel knife easily; geodes are common in basaltic volcanic regions, especially Brazil, Uruguay, Mexico, and the U.S. Midwest.
