mineral
Polished agate geode slice
Microcrystalline quartz (chalcedony), SiO₂
AI-generated identification · may be incorrectHardness 6.5–7 Mohs; gray, cream, and brown translucent-to-opaque bands with a waxy to glassy luster. The cut face is polished; the orange-yellow outer rim may be natural iron staining or a colored coating, and the visible image does not establish crystal structure or cleavage.
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Physical properties
Hardness 6.5–7 Mohs; gray, cream, and brown translucent-to-opaque bands with a waxy to glassy luster. The cut face is polished; the orange-yellow outer rim may be natural iron staining or a colored coating, and the visible image does not establish crystal structure or cleavage.
Formation & geological history
Agate forms as silica-rich fluids deposit chalcedony in cavities, commonly in volcanic rock; deposits range from ancient to geologically recent. This specimen has been cut and polished.
Uses & applications
Used for jewelry, ornaments, and collecting; small slices are often sold as decorative specimens.
Geological facts
Agate is a banded variety of chalcedony, and its patterns reflect successive mineral deposits in a cavity.
Field identification & locations
Look for curved or concentric bands and a fine-grained, non-cleaving surface; common sources include Brazil, Uruguay, and the United States. The bright rim may be treated, so inspect before buying.
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