mineral

Banded agate (likely brown/gray chalcedony)

Microcrystalline quartz, SiO₂ (chalcedony/agate)

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; gray, brown, cream, and possibly reddish bands with a waxy to vitreous luster. Quartz has a trigonal structure, no cleavage, conchoidal fracture, and specific gravity near 2.6; the rounded shape appears naturally weathered or tumbled.

Identified August 12, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rocks, depositing successive layers of chalcedony and quartz. Individual agate bands may form over thousands to millions of years, commonly in basaltic volcanic terrains.

Uses & applications

Used for cabochons, beads, carvings, polished stones, bookends, and decorative objects; this small rough specimen has modest commercial value.

Geological facts

Agate’s distinctive banding results from changing impurities and fluid chemistry during cavity filling. Fine translucent banding and strong contrast generally increase desirability.

Field identification & locations

Look for translucent edges, curved/concentric banding, waxy luster, and conchoidal fracture; a steel file should not easily scratch it. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the western United States.