gemstone

Polished agate or chalcedony cabochon

Microcrystalline quartz (SiO₂), likely agate/chalcedony with dark dendritic or mineral inclusions

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; gray-green translucent body with a glossy vitreous-to-waxy luster and black internal inclusions or matrix. Quartz has a trigonal crystal structure, but the specimen is cryptocrystalline and shows no visible cleavage.

Identified September 8, 2026More gemstone →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rocks, commonly during the Cenozoic or older geologic episodes; successive silica deposition can create agate banding and inclusion patterns.

Uses & applications

Used as a polished cabochon, bead, or collectible gemstone; durable for jewelry and ornamental objects. Common material is inexpensive, while distinctive natural patterns may command more.

Geological facts

The image most strongly suggests a tumbled or cabochon-cut chalcedony/agate, though exact identification requires testing and examination of the hidden surfaces.

Field identification & locations

Commonly found in volcanic regions such as Brazil, Uruguay, Mexico, Madagascar, India, and the western United States. Field clues include waxy luster, translucency, conchoidal fracture, and lack of cleavage; a quartz hardness test should scratch glass.