mineral
Tumbled agate/chalcedony
Microcrystalline quartz (SiO₂), likely banded chalcedony or agate
AI-generated identification · may be incorrectHardness 6.5–7 Mohs; translucent cream, gray, tan, and brown with subtle curved banding; waxy to glassy luster; cryptocrystalline quartz with no visible cleavage; specific gravity about 2.58–2.64.
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Physical properties
Hardness 6.5–7 Mohs; translucent cream, gray, tan, and brown with subtle curved banding; waxy to glassy luster; cryptocrystalline quartz with no visible cleavage; specific gravity about 2.58–2.64.
Formation & geological history
Forms when silica-rich groundwater fills cavities in volcanic rock, depositing chalcedony and quartz in successive layers. The specimen is likely a naturally weathered or tumbled fragment; its precise geological age cannot be determined visually.
Uses & applications
Used for ornamental stones, cabochons, carvings, beads, and lapidary work; attractive pieces have modest collector value.
Geological facts
Agate is a variety of chalcedony distinguished by banding, while unbanded translucent material is called chalcedony. Iron and other impurities produce the tan, brown, and reddish colors.
Field identification & locations
Identify by its waxy translucence, very fine texture, curved layering, lack of cleavage, and ability to scratch glass. Common sources include Brazil, Uruguay, India, Mexico, Madagascar, and the western United States.
