mineral
Tumbled agate or chalcedony
Microcrystalline quartz, SiO₂
AI-generated identification · may be incorrectSmooth, rounded, translucent gray-brown specimen with waxy to dull luster and possible subtle banding. Hardness 6.5–7 Mohs; no cleavage; conchoidal fracture; trigonal quartz structure; specific gravity about 2.6.
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Physical properties
Smooth, rounded, translucent gray-brown specimen with waxy to dull luster and possible subtle banding. Hardness 6.5–7 Mohs; no cleavage; conchoidal fracture; trigonal quartz structure; specific gravity about 2.6.
Formation & geological history
Forms when silica-rich groundwater deposits chalcedony and quartz in cavities, commonly within volcanic rocks; individual specimens may range from Paleozoic to recent. The polished shape indicates human tumbling and abrasion.
Uses & applications
Used for beads, cabochons, paperweights, and decorative objects; common tumbled pieces have modest collector value.
Geological facts
Agate is a variety of chalcedony distinguished by curved or layered color bands, while uniformly colored material is generally called chalcedony. The image may also represent polished jasper or another quartz-rich stone, which cannot be confirmed visually alone.
Field identification & locations
Test with a steel file or quartz reference: it should resist scratching by steel and may scratch glass. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the United States.
