gemstone

Tumbled brown chalcedony (likely carnelian/agate)

Microcrystalline quartz, SiO₂; chalcedony with iron-oxide coloration

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent to opaque reddish-brown, with a waxy to vitreous luster and no visible cleavage. Its rounded, polished form and possible subtle internal banding are typical of tumbled chalcedony or agate.

Identified September 15, 2026More gemstone →

Explore Tumbled brown chalcedony (likely carnelian/agate) in the encyclopedia →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities and fractures in volcanic rocks, later becoming microcrystalline quartz; iron oxides create the brown-red color. Deposits range from Cenozoic to much older volcanic-hosted formations.

Uses & applications

Used for beads, cabochons, carvings, ornamental objects, and inexpensive jewelry; durable enough for everyday wear.

Geological facts

Carnelian is the orange-red variety of chalcedony, while brown material may be called sard or brown agate depending on translucency and banding. Heating can intensify iron-related coloration.

Field identification & locations

Commonly found in India, Brazil, Uruguay, Madagascar, Germany, and the western United States. Identify by its smooth waxy surface, lack of cleavage, hardness sufficient to scratch glass, and conchoidal fracture; definitive identification may require magnification or testing.