mineral
Polished white-and-brown chalcedony (likely agate/jasper)
Microcrystalline quartz, SiO₂; chalcedony with iron-oxide staining or jasperous inclusions
AI-generated identification · may be incorrectHardness about 6.5–7 Mohs; white to cream with rusty brown patches, waxy-to-glassy luster, cryptocrystalline quartz structure, and no obvious cleavage. The smoothly polished surface indicates a shaped or tumbled specimen.
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Physical properties
Hardness about 6.5–7 Mohs; white to cream with rusty brown patches, waxy-to-glassy luster, cryptocrystalline quartz structure, and no obvious cleavage. The smoothly polished surface indicates a shaped or tumbled specimen.
Formation & geological history
Forms when silica-rich groundwater fills cavities and fractures in volcanic rock, with iron oxides producing the brown coloration; commonly Cenozoic to older, depending on the host deposit. Exact age and locality cannot be determined from the image.
Uses & applications
Used for cabochons, carvings, beads, ornaments, and lapidary material; durable but not generally high-value gemstone material.
Geological facts
Agate and jasper overlap texturally: agate is typically more translucent and banded, while jasper is opaque and mottled. The specimen appears predominantly opaque, so jasper or jasper-rich chalcedony is plausible.
Field identification & locations
Identify by its fine texture, quartz-like hardness, lack of cleavage, and resistance to scratching by steel; glass can help test hardness, though polished surfaces make testing undesirable. Common sources include Brazil, Uruguay, India, Madagascar, Mexico, and the western United States.
