metamorphic
Polished orbicular jasper (likely kambaba jasper)
Silicified microcrystalline quartz/chalcedony, commonly with chlorite- or amphibole-rich orbicules; composition varies
AI-generated identification · may be incorrectHardness about 6.5–7 Mohs; dark green to black with brown-red patches and rounded green orbicules, a waxy-to-glassy luster, and no visible cleavage. The specimen is highly polished and its exact identity cannot be confirmed from appearance alone.
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Physical properties
Hardness about 6.5–7 Mohs; dark green to black with brown-red patches and rounded green orbicules, a waxy-to-glassy luster, and no visible cleavage. The specimen is highly polished and its exact identity cannot be confirmed from appearance alone.
Formation & geological history
Formed by silica-rich fluids replacing or cementing volcanic material, with orbicules developing during alteration; commonly Precambrian or older, depending on locality. Kambaba jasper is especially associated with Madagascar.
Uses & applications
Used as a cabochon, lapidary ornament, worry stone, or decorative polished stone; not generally used as structural stone. Common polished pieces typically sell for about $10–$40, with larger or unusually patterned specimens reaching $50–$100.
Geological facts
The circular markings are orbicules, produced by concentric mineral growth or alteration rather than fossils. “Jasper” is a trade term for opaque, impurity-rich chalcedony and can encompass several visually similar materials.
Field identification & locations
Identify it by its opaque dark-green body, rounded mottling, fine-grained texture, and quartz-like hardness; a scratch test, streak test, and locality information help distinguish it from serpentine, basalt, or dyed stone. Common sources include Madagascar, South Africa, Australia, and Mexico.
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