mineral
Tumbled chalcedony (likely brown agate/jasper)
Microcrystalline quartz, SiO₂; potentially iron-stained chalcedony or jasper
AI-generated identification · may be incorrectOpaque to translucent tan-brown with waxy luster, smooth tumbled surfaces, and subtle banding; Mohs hardness 6.5–7, no cleavage, conchoidal fracture, and quartz crystal structure at microscopic scale. The image does not show enough detail for a definitive variety identification.
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Physical properties
Opaque to translucent tan-brown with waxy luster, smooth tumbled surfaces, and subtle banding; Mohs hardness 6.5–7, no cleavage, conchoidal fracture, and quartz crystal structure at microscopic scale. The image does not show enough detail for a definitive variety identification.
Formation & geological history
Forms when silica-rich groundwater fills cavities, fractures, or vesicles in volcanic rocks; iron oxides create the brown coloration. Such material commonly formed during Cenozoic or older volcanic activity, depending on locality.
Uses & applications
Used for cabochons, beads, carvings, polished stones, and lapidary display; tougher opaque material may be sold as jasper.
Geological facts
Agate is banded chalcedony, whereas jasper is generally opaque and impure; many commercial pieces are labeled broadly as “brown agate” or “jasper.”
Field identification & locations
Identify by its glassy-to-waxy appearance, strong scratch resistance, lack of cleavage, and conchoidal break; it should not be scratched by a steel knife easily. Common sources include Brazil, Uruguay, Mexico, Madagascar, India, and the western United States.
