mineral
Tumbled/rounded agate (likely mossy or brecciated chalcedony)
Microcrystalline quartz, SiO₂ (chalcedony/agate)
AI-generated identification · may be incorrectHardness 6.5–7 Mohs; blue-gray to brown with translucent chalcedony, rusty iron-oxide staining, waxy to vitreous luster, and no visible cleavage. The rounded, water-worn surface appears naturally polished; internal banding is indistinct, so exact identification from the photo is limited.
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Physical properties
Hardness 6.5–7 Mohs; blue-gray to brown with translucent chalcedony, rusty iron-oxide staining, waxy to vitreous luster, and no visible cleavage. The rounded, water-worn surface appears naturally polished; internal banding is indistinct, so exact identification from the photo is limited.
Formation & geological history
Silica-rich groundwater filled cavities and fractures in volcanic rock, later forming chalcedony and agate over millions of years; iron oxides produced the brown inclusions. The specimen was likely eroded and rounded in a river, beach, or gravel deposit.
Uses & applications
Used as a lapidary stone for cabochons, carvings, bookends, and ornamental objects; attractive examples are collected or polished for jewelry.
Geological facts
Agate is a variety of chalcedony distinguished by banding or patterned inclusions. The blue-gray material may also be jaspery chalcedony if it lacks true agate banding.
Field identification & locations
Test for glassy translucence at thin edges, very high scratch resistance, and conchoidal fracture; it should not scratch readily with a steel knife. Common in volcanic terrains and alluvial gravels worldwide.
