mineral
Polished brown agate or jasper
Microcrystalline quartz, SiO₂ (chalcedony variety; exact identification uncertain)
AI-generated identification · may be incorrectDark brown, opaque to slightly translucent, with a glossy polished surface and fine-grained texture; quartz hardness is about 6.5–7 Mohs, no visible cleavage, conchoidal fracture, and specific gravity near 2.6. The specimen may contain iron-oxide staining or inclusions.
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Physical properties
Dark brown, opaque to slightly translucent, with a glossy polished surface and fine-grained texture; quartz hardness is about 6.5–7 Mohs, no visible cleavage, conchoidal fracture, and specific gravity near 2.6. The specimen may contain iron-oxide staining or inclusions.
Formation & geological history
Forms when silica-rich groundwater fills cavities and fractures in volcanic rocks, followed by slow deposition of chalcedony and quartz. Its precise geological age cannot be determined from the photograph; agates and jaspers occur from Precambrian to recent rocks.
Uses & applications
Used for cabochons, carvings, beads, ornaments, and lapidary collectibles; jasper and agate are also used decoratively in tiles and small architectural objects.
Geological facts
Agate typically shows banding or translucency, whereas jasper is more uniformly opaque and earthy. The strong polish and rounded edges indicate human lapidary processing.
Field identification & locations
Commonly found in volcanic terrains, especially Brazil, Uruguay, India, Madagascar, Mexico, and the western United States. Check hardness, streak, translucency at thin edges, and internal banding; iron-rich brown coloration alone is not diagnostic.
