mineral

Tumbled chalcedony (likely gray/brown agate)

Microcrystalline quartz, SiO₂ (chalcedony; possible agate variety)

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent gray-brown body with whitish cloudy zones, vitreous to waxy luster, and no visible cleavage. Specific gravity is about 2.58–2.65; the rounded surface indicates tumbling and polishing.

Identified August 9, 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 over time. It is commonly Cenozoic to older, with age dependent on the host rock and deposit.

Uses & applications

Used for beads, cabochons, carvings, ornamental stones, and lapidary collections; less commonly as aggregate. Its value is primarily decorative rather than industrial.

Geological facts

Chalcedony is quartz whose crystals are too small to see individually; agate is typically identified by distinct rhythmic banding, which is not strongly apparent here.

Field identification & locations

Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the western United States. Identify it by its waxy translucence, quartz hardness, conchoidal fracture, and inability to scratch with a steel knife; a definitive variety identification may require microscopy.