mineral
Tumbled brown agate/chalcedony (probable)
Microcrystalline quartz, SiO₂; likely iron-stained agate or jasper
AI-generated identification · may be incorrectHardness 6.5–7 Mohs; brown, reddish, gray, and cream coloration with faint curved banding; waxy to vitreous luster; cryptocrystalline quartz with no visible cleavage. The smooth rounded surface indicates tumbling and polishing.
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Physical properties
Hardness 6.5–7 Mohs; brown, reddish, gray, and cream coloration with faint curved banding; waxy to vitreous luster; cryptocrystalline quartz with no visible cleavage. The smooth rounded surface indicates tumbling and polishing.
Formation & geological history
Forms when silica-rich groundwater fills cavities in volcanic rocks, depositing successive layers of chalcedony and quartz; coloration commonly comes from iron oxides. Individual specimens may range from Paleozoic to Cenozoic, depending on locality.
Uses & applications
Used as an inexpensive ornamental stone, cabochon, bead, paperweight, or lapidary material. Common polished pieces generally have modest commercial value.
Geological facts
Agate is a variety of chalcedony distinguished by banding, while jasper is more opaque and typically lacks obvious bands. The photograph alone cannot reliably separate agate from jasper or other brown chalcedony.
Field identification & locations
Common worldwide, including Brazil, Uruguay, Mexico, India, Madagascar, and the western United States. Look for translucent edges, curved layering, waxy luster, and resistance to scratching by steel; definitive identification may require a loupe or testing.
