gemstone

Polished agate (likely banded chalcedony)

Microcrystalline quartz, SiO₂ (chalcedony/agate)

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; white, cream, gray, and pale pink translucent bands with a waxy to vitreous luster. Quartz is trigonal but forms cryptocrystalline masses, typically without visible cleavage; specific gravity is about 2.60–2.65.

Identified August 30, 2026More gemstone →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rock, depositing successive layers of chalcedony and quartz. Individual bands may record changing fluids over millions of years, commonly during the Cenozoic or older volcanic episodes.

Uses & applications

Used for cabochons, beads, carvings, ornaments, and small tumbled specimens; durable aggregate and decorative stone are additional uses.

Geological facts

The concentric, curved banding and translucency are characteristic of agate, while the smooth shape indicates tumbling or polishing.

Field identification & locations

Identify it by testing for glassy translucency, curved internal bands, and quartz-like hardness; it should scratch ordinary glass but not steel easily. Common sources include Brazil, Uruguay, India, Mexico, Madagascar, and the United States.