gemstone

Polished dark chalcedony or agate cabochon

Cryptocrystalline quartz, SiO₂; likely brown-red chalcedony/agate

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; smooth vitreous-to-waxy luster, opaque to translucent, dark brown-red color, and no visible cleavage. The domed cabochon appears polished and mounted in a metal setting; internal banding is not visible.

Identified September 3, 2026More gemstone →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rocks, precipitating microscopic quartz fibers over time; commonly Cenozoic to older, depending on the host rock. Exact identification and age require examination outside the setting.

Uses & applications

Used for inexpensive jewelry, cabochons, carvings, and ornamental objects. Usually valued more for color, pattern, and workmanship than rarity.

Geological facts

The image may also represent jasper, a fully opaque chalcedony variety, or dyed material; the red-brown color alone is not diagnostic.

Field identification & locations

Check for natural banding, conchoidal fracture, and glass-scratching hardness; inspect under magnification for dye concentration in cracks. Common sources include Brazil, Uruguay, India, Madagascar, Mexico, and the United States.