mineral

Banded agate (chalcedony)

Microcrystalline quartz, SiO₂; agate variety of chalcedony

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; typically gray, white, tan, or reddish-brown with fine concentric or wavy bands. Waxy to vitreous luster, cryptocrystalline structure, no cleavage, and specific gravity about 2.6.

Identified August 15, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater repeatedly fills cavities in volcanic rock, depositing layered chalcedony and occasional quartz. Most examples formed during the Cenozoic or Mesozoic, though age depends on locality.

Uses & applications

Used for cabochons, slabs, carvings, beads, bookends, and decorative objects; thin slices are prized for polished displays. Common pieces have modest value, while sharply patterned specimens can be collectible.

Geological facts

The visible banding reflects changing chemistry, impurities, and growth conditions during successive silica deposits. The rough, pale matrix and translucent layered interior are characteristic of agate rather than ordinary massive quartz.

Field identification & locations

Identify it by translucent edges, curved or wavy internal banding, waxy luster, and inability to scratch it with a steel knife; it should scratch glass. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the western United States.