metamorphic
Orbicular jasper (likely ocean jasper)
Siliceous microcrystalline quartz/chalcedony with iron-oxide and other mineral orbicules; composition varies
AI-generated identification · may be incorrectPolished, opaque green-gray matrix with pink-red circular orbicules and dark rims; quartz hardness about 6.5–7 Mohs, glassy to waxy luster, no visible cleavage, microcrystalline structure. The specimen appears shaped and polished.
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Physical properties
Polished, opaque green-gray matrix with pink-red circular orbicules and dark rims; quartz hardness about 6.5–7 Mohs, glassy to waxy luster, no visible cleavage, microcrystalline structure. The specimen appears shaped and polished.
Formation & geological history
Forms through silica-rich volcanic or hydrothermal processes, with rhythmic mineral growth producing orbicules; Madagascar ocean jasper is commonly Miocene–Cenozoic, though similar orbicular jaspers occur elsewhere.
Uses & applications
Used for cabochons, carvings, display pieces, and lapidary art; not typically used as structural stone. Value depends on pattern, polish, provenance, and size.
Geological facts
The circular “orbs” are mineral aggregates rather than fossils; strong orbicular patterning is especially prized by collectors.
Field identification & locations
Identify by its opaque chalcedony matrix, concentric or radiating orbicules, hardness, and resistance to scratching by steel. Common sources include Madagascar, Mexico, Australia, and Oregon; acid testing and microscopy can distinguish it from dyed stone.
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