mineral
Polished agate or jasper pebble
Microcrystalline quartz (chalcedony), SiO₂, possibly iron-oxide-bearing
AI-generated identification · may be incorrectHardness about 6.5–7 Mohs; orange-brown, translucent to opaque, with a waxy to glassy luster and fine cryptocrystalline structure. The rounded, glossy surface indicates tumbling or polishing; visible banding is limited, so jasper is also possible.
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Physical properties
Hardness about 6.5–7 Mohs; orange-brown, translucent to opaque, with a waxy to glassy luster and fine cryptocrystalline structure. The rounded, glossy surface indicates tumbling or polishing; visible banding is limited, so jasper is also possible.
Formation & geological history
Formed when silica-rich groundwater filled cavities or fractures in volcanic rock, later colored by iron oxides. Chalcedony deposits range from Paleozoic to recent; the specimen’s exact age and locality cannot be determined from the image.
Uses & applications
Used for cabochons, beads, carvings, paperweights, and decorative objects; common polished pieces have modest collecting value.
Geological facts
Agate and jasper are varieties of chalcedony distinguished mainly by appearance: agate is typically translucent and banded, while jasper is more opaque and massive.
Field identification & locations
Look for hardness sufficient to scratch glass, a smooth waxy or glassy surface, and absence of cleavage; iron staining produces orange-red tones. Common sources include Brazil, Uruguay, India, Madagascar, Mexico, and the western United States.
