mineral
Polished brecciated jasper or agate
Microcrystalline quartz (chalcedony), SiO₂, with iron-oxide and possibly carbonate inclusions
AI-generated identification · may be incorrectHardness about 6.5–7 Mohs; tan, brown, cream, and gray coloration with a glossy polished luster and swirling/brecciated patterns. Quartz has no cleavage, conchoidal fracture, and specific gravity around 2.6.
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Physical properties
Hardness about 6.5–7 Mohs; tan, brown, cream, and gray coloration with a glossy polished luster and swirling/brecciated patterns. Quartz has no cleavage, conchoidal fracture, and specific gravity around 2.6.
Formation & geological history
Formed when silica-rich groundwater deposited chalcedony in cavities or fractures, commonly incorporating iron oxides and cementing fragmented material; age depends on locality, often Cenozoic to older volcanic-host-rock sequences.
Uses & applications
Used as a lapidary and ornamental stone for cabochons, carvings, polished slices, and display specimens; generally not used structurally.
Geological facts
The specimen appears human-polished, so surface texture may obscure natural fracture and luster. Stronger red-brown colors typically reflect hematite or limonite inclusions.
Field identification & locations
Identify by its waxy-to-glassy polish, opaque patterned body, lack of cleavage, and inability to scratch it with a steel knife; quartz should scratch ordinary glass. Common sources include Brazil, Madagascar, Mexico, India, and the western United States.
