mineral

Tumbled brown agate (chalcedony)

Microcrystalline quartz, SiO₂; likely iron-stained chalcedony

AI-generated identification · may be incorrect

Polished, translucent-to-opaque brown stone with a waxy to vitreous luster. Quartz hardness is 6.5–7 Mohs; crystals are too fine to see, and agate typically has no visible cleavage.

Identified October 16, 2026More mineral →

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Physical properties

Polished, translucent-to-opaque brown stone with a waxy to vitreous luster. Quartz hardness is 6.5–7 Mohs; crystals are too fine to see, and agate typically has no visible cleavage.

Formation & geological history

Agate forms as silica-rich fluids fill cavities and fractures, depositing layered chalcedony; iron oxides can produce brown coloration. It occurs in volcanic and other silica-rich settings across many geological ages.

Uses & applications

Used for beads, cabochons, ornaments, and small decorative objects; common tumbled pieces are primarily collectible curios.

Geological facts

Agate is a variety of chalcedony, itself a microcrystalline form of quartz; distinctive banding may be subtle or absent in small polished pieces.

Field identification & locations

The image shows a smooth, rounded, brown specimen, but no diagnostic banding is visible, so identification as agate is tentative. Agates occur worldwide, notably in Brazil, Uruguay, India, and the United States.