mineral
Polished agate (likely banded/chalcedony agate)
Microcrystalline quartz, SiO₂; agate variety of chalcedony
AI-generated identification · may be incorrectMohs hardness 6.5–7; brown, cream, gray, and reddish areas with a waxy to vitreous luster. Fine-grained quartz with no visible cleavage; the polished surface obscures internal banding and crystal structure.
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Physical properties
Mohs hardness 6.5–7; brown, cream, gray, and reddish areas with a waxy to vitreous luster. Fine-grained quartz with no visible cleavage; the polished surface obscures internal banding and crystal structure.
Formation & geological history
Forms as silica-rich fluids fill cavities and cracks, depositing successive layers of chalcedony; agates occur in volcanic rocks and sedimentary settings across many geological ages.
Uses & applications
Used for jewelry, ornaments, and lapidary work; this small polished piece is primarily decorative or collectible.
Geological facts
Agate’s colors and patterns result from trace impurities and changing conditions during silica deposition.
Field identification & locations
Identify by its hard, silica-rich surface and possible translucent, layered zones; common sources include Brazil, Uruguay, India, and the United States. Approximate value: $2–$15 for a small common polished piece.
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