mineral

Polished banded agate (likely sardonyx)

Cryptocrystalline chalcedony, SiO₂; reddish bands are iron-stained layers

AI-generated identification · may be incorrect

Mohs hardness 6.5–7; reddish-brown, white, and gray concentric banding; waxy to vitreous luster; microcrystalline quartz with no visible cleavage; specific gravity about 2.6.

Identified August 8, 2026More mineral →

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Physical properties

Mohs hardness 6.5–7; reddish-brown, white, and gray concentric banding; waxy to vitreous luster; microcrystalline quartz with no visible cleavage; specific gravity about 2.6.

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rock, depositing successive chalcedony layers; banding commonly developed during the Cenozoic, though agates occur in rocks of many ages.

Uses & applications

Used for cabochons, beads, carvings, paperweights, and decorative polished specimens; generally ornamental rather than industrial.

Geological facts

The rounded shape and glossy surface indicate tumbling or polishing. “Sardonyx” technically refers to layered red-brown and white chalcedony, while broader irregular banding is commonly marketed as banded agate.

Field identification & locations

Identify it by hardness, translucent edges, waxy luster, and curved continuous bands; it should not fizz in dilute acid. Common sources include Brazil, Uruguay, India, Madagascar, Mexico, and the western United States.