mineral
Polished banded agate (probable)
Microcrystalline quartz, SiO₂ (chalcedony/agate)
AI-generated identification · may be incorrectHardness 6.5–7 Mohs; translucent gray, cream, brown, and black curved banding with a vitreous to waxy luster. Agate is cryptocrystalline quartz and commonly has no visible cleavage; specific gravity is about 2.6.
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Physical properties
Hardness 6.5–7 Mohs; translucent gray, cream, brown, and black curved banding with a vitreous to waxy luster. Agate is cryptocrystalline quartz and commonly has no visible cleavage; specific gravity is about 2.6.
Formation & geological history
Forms when silica-rich groundwater fills cavities in volcanic rock, depositing successive chalcedony and quartz bands. Individual bands may range from Paleozoic to recent in age, depending on the host rock and locality.
Uses & applications
Cut and polished for cabochons, beads, ornaments, bookends, and lapidary specimens; its durability makes it suitable for jewelry and decorative objects.
Geological facts
The dark areas may be iron- or manganese-rich inclusions, or natural dendritic patterns; dyeing is also common in commercial agate, though this piece’s colors appear plausibly natural.
Field identification & locations
Identify by curved or concentric banding, translucency, waxy polish, and resistance to scratching with steel. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the United States.
