
sedimentary
Polished Ocean Jasper (orbicular jasper)
Siliceous microcrystalline quartz/chalcedony, mainly SiO₂, with iron- and manganese-rich inclusions
AI-generated identification · may be incorrectHardness about 6.5–7 Mohs; opaque, waxy to glassy luster, with green-gray, pink, cream, and reddish orbicular patterns. It has cryptocrystalline quartz structure and no visible cleavage; specific gravity is roughly 2.55–2.70.
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Physical properties
Hardness about 6.5–7 Mohs; opaque, waxy to glassy luster, with green-gray, pink, cream, and reddish orbicular patterns. It has cryptocrystalline quartz structure and no visible cleavage; specific gravity is roughly 2.55–2.70.
Formation & geological history
Forms when silica-rich volcanic or hydrothermal fluids replace or cement earlier volcanic material, producing concentric orbicules and iron-oxide coloration. Most commercial Ocean Jasper comes from Oligocene–Miocene volcanic rocks of Madagascar, roughly 5–30 million years old.
Uses & applications
Used for cabochons, carvings, beads, polished pieces, and decorative objects; value is primarily ornamental and collectible rather than industrial.
Geological facts
Its distinctive “orbicular” spots are radial or concentric growth structures, not fossils. The name Ocean Jasper is a trade name associated especially with coastal Madagascar deposits.
Field identification & locations
Identify it by its hard, opaque chalcedony body and rounded pink, red, cream, or green orbicules; it should resist scratching by a steel knife. Common sources include Madagascar, Mexico, Australia, and Oregon.
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