mineral
Polished banded agate
Agate, a banded variety of chalcedony (microcrystalline SiO₂)
AI-generated identification · may be incorrectMohs hardness 6.5–7; orange, cream, and white curved bands with a waxy-to-vitreous luster. Trigonal quartz structure at microscopic scale; no visible cleavage, conchoidal fracture; specific gravity about 2.6.
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Physical properties
Mohs hardness 6.5–7; orange, cream, and white curved bands with a waxy-to-vitreous luster. Trigonal quartz structure at microscopic scale; no visible cleavage, conchoidal fracture; specific gravity about 2.6.
Formation & geological history
Silica-rich fluids deposited successive layers in cavities, commonly in volcanic rock; agate forms over geological time, often during cooling and alteration of ancient lavas.
Uses & applications
Used for cabochons, beads, ornaments, and small carvings; durable and popular with collectors.
Geological facts
Agate’s bands record changing conditions as silica accumulated, and some patterns resemble landscapes or “fortification” walls.
Field identification & locations
Look for translucent chalcedony with distinct curved or concentric bands; common in volcanic regions worldwide, including Brazil, Uruguay, India, and the western United States. Polished small specimens typically sell for about $5–$30, depending on pattern and size.
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