mineral
Banded agate (polished agate slice)
Agate, a variety of microcrystalline quartz (SiO₂; chalcedony)
AI-generated identification · may be incorrectHardness 6.5–7 Mohs; gray, white, and brown concentric bands with a vitreous-to-waxy luster. Microcrystalline quartz; no prominent cleavage, with a conchoidal fracture and typical specific gravity near 2.6.
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Physical properties
Hardness 6.5–7 Mohs; gray, white, and brown concentric bands with a vitreous-to-waxy luster. Microcrystalline quartz; no prominent cleavage, with a conchoidal fracture and typical specific gravity near 2.6.
Formation & geological history
Silica-rich groundwater deposited successive chalcedony layers in a cavity, likely in volcanic rock; the exact age and locality cannot be determined from the image.
Uses & applications
Used for jewelry, ornaments, lapidary work, and small decorative objects; agate is also collected for its banding.
Geological facts
Agate’s distinctive bands record changing conditions during silica deposition, and some layers may enclose a hollow or crystal-lined center.
Field identification & locations
Look for translucent chalcedony with curved, nested bands and a waxy polish; common sources include Brazil, Uruguay, India, and the United States. Value: roughly $5–$30 for a small polished slice, depending on size, pattern, and workmanship.
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