gemstone

Tumbled chalcedony (likely carnelian or brown agate)

Microcrystalline quartz, SiO₂; chalcedony with iron-oxide coloration

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent brown, honey, and reddish zones; waxy to vitreous luster; cryptocrystalline quartz with no visible cleavage, conchoidal fracture, and specific gravity about 2.6. Its smooth, rounded surface indicates mechanical tumbling and polishing.

Identified August 13, 2026More gemstone →

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

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities and fractures in volcanic or sedimentary rocks, with iron oxides producing red-brown colors; individual material may range from Precambrian to recent. The specimen’s exact locality and age cannot be determined from the image.

Uses & applications

Used for beads, cabochons, carvings, ornamental objects, and inexpensive collectible stones; durable enough for jewelry and decorative pieces.

Geological facts

The reddish variety is commonly called carnelian, while banded material is agate; these names overlap when color zoning is subtle. Chalcedony is a quartz-group mineral composed of extremely fine intergrowths of quartz varieties.

Field identification & locations

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