mineral

Tumbled brown chalcedony (likely smoky quartz or agate)

Chalcedony, microcrystalline SiO₂; exact variety cannot be confirmed visually

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; translucent brown to gray-brown, waxy to vitreous luster, cryptocrystalline quartz with no visible cleavage and conchoidal fracture. The smooth, rounded surface indicates tumbling or polishing.

Identified September 18, 2026More mineral →

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Physical properties

Formation & geological history

Silica-rich groundwater deposited quartz fibers in cavities or fractures, commonly in volcanic rocks; formation ages range from young to Paleozoic and older. Brown color may result from iron oxides or included smoky quartz.

Uses & applications

Used as a low-cost ornamental stone, cabochon, carving material, and lapidary specimen; commonly sold as a worry stone or tumbled stone. Typical value is modest unless pattern, translucency, or provenance is exceptional.

Geological facts

Chalcedony is quartz composed of extremely fine interlocking crystals, so crystal faces are usually absent. Brown varieties may be marketed as brown agate, smoky quartz, or chocolate chalcedony.

Field identification & locations

Identify by its glassy-to-waxy appearance, high hardness, lack of cleavage, and inability to scratch it with a steel knife; it should scratch glass. Common sources include Brazil, Uruguay, India, Madagascar, and the western United States.