metamorphic
Polished orbicular jasper (likely ocean jasper)
Silicified microcrystalline quartz/chalcedony; SiO₂, with iron-oxide inclusions
AI-generated identification · may be incorrectHardness about 6.5–7 Mohs; orange-brown, cream, and black mottling; opaque, waxy to vitreous luster, with no visible cleavage. The rounded shape is tumbled or polished rather than natural crystal form; black patterns may be manganese or iron oxides and other inclusions.
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Physical properties
Hardness about 6.5–7 Mohs; orange-brown, cream, and black mottling; opaque, waxy to vitreous luster, with no visible cleavage. The rounded shape is tumbled or polished rather than natural crystal form; black patterns may be manganese or iron oxides and other inclusions.
Formation & geological history
Formed when silica-rich fluids replaced or cemented volcanic material, preserving orbicular or brecciated textures; geological age depends on locality, commonly Paleozoic to Mesozoic. The specimen is probably Madagascar ocean jasper, though appearance alone cannot confirm locality.
Uses & applications
Used for cabochons, carvings, palm stones, beads, and decorative objects; it has little industrial use compared with ordinary quartz.
Geological facts
“Ocean jasper” is a trade name applied to patterned jasper, especially material from Madagascar. Its striking patterns arise from contrasting chalcedony, quartz, iron oxides, and sometimes feldspar or volcanic remnants.
Field identification & locations
Identify it by its opaque silica body, polished waxy surface, orange coloration, and irregular black dendritic or orbicular markings; it should not scratch easily with a steel knife. Common sources include Madagascar, Mexico, Australia, and the western United States.
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