mineral
Tumbled brown chalcedony (likely carnelian/agatesque material)
Microcrystalline quartz, SiO₂; chalcedony variety
AI-generated identification · may be incorrectHardness 6.5–7 Mohs; translucent brown to reddish-brown, waxy/glassy luster, cryptocrystalline structure, and no visible cleavage. The smooth glossy surface indicates tumbling or polishing; internal pale patches may be quartz or host material.
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Physical properties
Hardness 6.5–7 Mohs; translucent brown to reddish-brown, waxy/glassy luster, cryptocrystalline structure, and no visible cleavage. The smooth glossy surface indicates tumbling or polishing; internal pale patches may be quartz or host material.
Formation & geological history
Forms when silica-rich groundwater fills cavities and fractures in volcanic rocks, precipitating as chalcedony over millions of years, commonly during the Cenozoic or older volcanic episodes. The specimen’s exact locality and age cannot be determined visually.
Uses & applications
Used for beads, cabochons, carvings, lapidary ornaments, and collections; durable pieces may be used in jewelry. Common material generally has modest commercial value.
Geological facts
Brown chalcedony may be sold as brown agate, carnelian, smoky chalcedony, or jasper depending on translucency and pattern. Color can result from iron oxides or hydroxides.
Field identification & locations
Identify by its waxy luster, translucency at thin edges, conchoidal fracture, and inability to scratch with a steel knife; it should scratch ordinary glass. Common sources include Brazil, Uruguay, India, Madagascar, Mexico, and the western United States.
