mineral
Polished dendritic agate or jasper pebble
Microcrystalline quartz (SiO₂), likely chalcedony with iron-oxide inclusions
AI-generated identification · may be incorrectBrown-and-cream, opaque to slightly translucent, waxy to glassy luster, nonmetallic; hardness about 6.5–7 Mohs, no visible cleavage, cryptocrystalline quartz structure. The rounded shape indicates tumbling or natural abrasion.
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Physical properties
Brown-and-cream, opaque to slightly translucent, waxy to glassy luster, nonmetallic; hardness about 6.5–7 Mohs, no visible cleavage, cryptocrystalline quartz structure. The rounded shape indicates tumbling or natural abrasion.
Formation & geological history
Silica-rich groundwater filled cavities and fractures in volcanic rock, later depositing chalcedony and iron oxides; commonly formed during the Cenozoic or earlier, depending on locality.
Uses & applications
Used as a tumbled stone, cabochon, ornament, and lapidary material; attractive specimens may be collected, though this small piece has limited commercial value.
Geological facts
The white area may be quartz/chalcedony, while the dark brown material may be iron-stained jasper or agate. A glassy sheen and conchoidal fracture distinguish quartz-rich material from ordinary sedimentary rock.
Field identification & locations
Common in volcanic terrains and alluvial gravels, especially in Brazil, Uruguay, Mexico, India, Madagascar, and the western United States. Identify with a streak test, hardness test, and close inspection for translucency or banding; avoid scratching valuable specimens.
