mineral
Polished/tumbled brown stone, likely jasper or chert
Microcrystalline quartz (SiO₂), possibly iron-rich jasper or chert
AI-generated identification · may be incorrectHardness about 6.5–7 Mohs; chocolate-brown with darker patches, opaque, smooth rounded surface, and waxy to subvitreous luster. It has no visible cleavage and is composed of extremely fine quartz crystals.
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Physical properties
Hardness about 6.5–7 Mohs; chocolate-brown with darker patches, opaque, smooth rounded surface, and waxy to subvitreous luster. It has no visible cleavage and is composed of extremely fine quartz crystals.
Formation & geological history
Forms when silica-rich fluids replace or cement sediments, with iron oxides producing the brown coloration; commonly Precambrian to Cenozoic in age depending on source. The specimen has been mechanically tumbled or polished.
Uses & applications
Used for cabochons, beads, carvings, bookends, and decorative aggregate; small tumbled pieces have modest lapidary value.
Geological facts
Jasper and chert can be difficult to distinguish visually; jasper is generally more opaque and iron-stained, while chert may be more uniformly gray, brown, or translucent at thin edges.
Field identification & locations
Identify by its glassy/waxy polish, exceptional scratch resistance, opaque silica-rich body, and lack of fizz in dilute acid. Common worldwide, especially in sedimentary and volcanic terrains.
