mineral
Tumbled brown chalcedony (likely chert or agate)
Microcrystalline quartz, SiO₂ (chalcedony); exact variety is uncertain from the image
AI-generated identification · may be incorrectHardness about 6.5–7 Mohs; opaque to slightly translucent brown, with a waxy to dull luster and conchoidal fracture. It appears smoothly water-worn or tumbled, with subtle lighter chalcedony patches and no obvious cleavage.
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Physical properties
Hardness about 6.5–7 Mohs; opaque to slightly translucent brown, with a waxy to dull luster and conchoidal fracture. It appears smoothly water-worn or tumbled, with subtle lighter chalcedony patches and no obvious cleavage.
Formation & geological history
Silica-rich groundwater filled cavities or replaced material in volcanic or sedimentary rock, forming microcrystalline quartz over geological time. Chalcedony varieties range from Paleozoic to recent deposits.
Uses & applications
Used for cabochons, carvings, beads, tumbling, and decorative objects; industrial-grade chalcedony/chert is used as a silica source and historically for tools.
Geological facts
The specimen may be brown jasper, chert, or low-contrast agate rather than a precisely identifiable variety. A translucent edge, waxy feel, and resistance to scratching help distinguish chalcedony from softer brown stones.
Field identification & locations
Commonly found in volcanic cavities, sedimentary nodules, river gravels, and beaches worldwide, including Brazil, Uruguay, Mexico, India, and the United States. A steel file should not scratch it; quartz crystal or streak testing can confirm identification.
