mineral

Polished banded agate

Chalcedony (microcrystalline quartz), SiO₂

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent reddish-brown, cream, and gray bands with a waxy to glassy luster. Quartz has a trigonal structure but chalcedony forms fibrous cryptocrystalline masses; no cleavage, conchoidal fracture, specific gravity about 2.6.

Identified September 13, 2026More mineral →

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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 iron-stained material. Individual bands may form over long intervals, commonly in Paleozoic to Cenozoic volcanic terrains.

Uses & applications

Used for cabochons, beads, carvings, tumbled stones, and ornamental objects; durable but generally inexpensive.

Geological facts

The curved, parallel banding and translucency are characteristic of agate; reddish colors commonly reflect iron oxides. The specimen appears cut and polished rather than naturally weathered.

Field identification & locations

Identify by testing glass resistance, observing curved bands under light, and checking its cool, hard, waxy surface; common sources include Brazil, Uruguay, Mexico, India, and the United States. Avoid confusing it with dyed glass or resin.