mineral
Polished brown chalcedony (likely carnelian or jasper)
Microcrystalline quartz, SiO₂; iron oxides produce the brown coloration
AI-generated identification · may be incorrectHardness 6.5–7 Mohs; brown to reddish-brown, waxy to vitreous luster, massive cryptocrystalline structure, and no visible cleavage. The rounded surface indicates tumbling or natural water wear.
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Physical properties
Hardness 6.5–7 Mohs; brown to reddish-brown, waxy to vitreous luster, massive cryptocrystalline structure, and no visible cleavage. The rounded surface indicates tumbling or natural water wear.
Formation & geological history
Forms when silica-rich groundwater fills cavities and fractures, with iron staining creating brown-red colors; commonly Cenozoic to older volcanic or sedimentary settings.
Uses & applications
Used for cabochons, beads, carvings, decorative stones, and inexpensive collector specimens; its durability suits jewelry.
Geological facts
Chalcedony is quartz made of extremely fine intergrown crystals. The specimen may be classified as brown carnelian if translucent, or jasper if strongly opaque and impurity-rich.
Field identification & locations
Identify by its smooth waxy surface, high hardness, conchoidal fracture, and resistance to scratching by steel; it should not fizz in dilute acid. Common sources include India, Brazil, Madagascar, Uruguay, and the western United States.
