metamorphic
Orbicular jasper / brecciated jasper
Silica-rich microcrystalline quartz (chalcedony), commonly with iron oxides and altered volcanic fragments
AI-generated identification · may be incorrectTypically hardness 6.5–7 Mohs, opaque, with black, tan, cream, and reddish-brown patches; dull to waxy luster and no visible cleavage. The specimen appears polished or naturally water-worn, with contrasting orbicular/brecciated textures.
Identified More metamorphic →
Explore Orbicular jasper / brecciated jasper in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Typically hardness 6.5–7 Mohs, opaque, with black, tan, cream, and reddish-brown patches; dull to waxy luster and no visible cleavage. The specimen appears polished or naturally water-worn, with contrasting orbicular/brecciated textures.
Formation & geological history
Forms when silica-rich fluids replace or cement altered volcanic rock, producing jasper, breccia, and orb-like mineral patterns. Usually associated with ancient volcanic terrains, commonly Paleozoic to Mesozoic or older depending on locality.
Uses & applications
Used as ornamental stone, cabochons, carvings, polished slabs, and lapidary collectibles; too variable and fractured for most construction use.
Geological facts
The black areas may be magnetite, manganese oxides, or dark silica, while cream and brown zones commonly contain quartz, clay minerals, and iron oxides. Exact identification requires a fresh surface, hardness testing, and ideally petrographic or chemical analysis.
Field identification & locations
Look for opaque cryptocrystalline silica, conchoidal fracture, and a quartz-like hardness that resists a steel knife. Similar material occurs in volcanic regions worldwide, including Oregon, California, Mexico, Madagascar, and Australia.
More like this
