mineral

Tumbled brown-and-olive chalcedony

Chalcedony, microcrystalline quartz (SiO₂), possibly jasper or brown agate

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent brown, olive, gray, and cream coloring; waxy to dull luster; cryptocrystalline quartz with no visible cleavage and conchoidal fracture. The rounded shape indicates tumbling or natural abrasion.

Identified August 26, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities and fractures in volcanic rocks, precipitating microscopic quartz fibers; coloration commonly comes from iron and other impurities. Individual specimens may range from Cenozoic to much older, depending on the host rock.

Uses & applications

Used for carvings, cabochons, beads, polished stones, and lapidary ornaments; attractive material has modest gemstone and collector appeal.

Geological facts

Chalcedony is quartz whose crystals are too small to see unaided; “jasper” generally refers to opaque, impure varieties, while “agate” typically shows distinct banding.

Field identification & locations

Identify by its glassy-to-waxy appearance, lack of cleavage, hardness, and inability to scratch it with a steel knife; quartz or glass can scratch it. Common worldwide, including Brazil, Uruguay, India, Madagascar, Mexico, and the western United States.