igneous
Polished ocean jasper (orbicular jasper), likely
Silica-rich microcrystalline quartz/chalcedony aggregate, commonly with feldspar, epidote, and iron oxides; composition varies
AI-generated identification · may be incorrectHardness about 6.5–7 Mohs; rounded polished pebble with blue-green, gray, cream, and dark orbicular patches, opaque, and waxy to glassy luster. No visible cleavage; fine cryptocrystalline structure.
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Physical properties
Hardness about 6.5–7 Mohs; rounded polished pebble with blue-green, gray, cream, and dark orbicular patches, opaque, and waxy to glassy luster. No visible cleavage; fine cryptocrystalline structure.
Formation & geological history
Forms through silica-rich volcanic or hydrothermal alteration, where chalcedony and other minerals fill cavities or develop orbicular patterns; many ocean jasper specimens formed in Oligocene–Miocene volcanic rocks of Madagascar.
Uses & applications
Used for cabochons, beads, carvings, polished stones, and collectors’ specimens; generally ornamental rather than industrial.
Geological facts
“Ocean jasper” is a trade name, not a single precisely defined mineral species; its distinctive orbicular patterns are the primary appeal.
Field identification & locations
Identify by testing hardness against glass, observing the opaque chalcedony-like body and patterned swirls, and checking for dyed color or resin treatment. Classic ocean jasper is associated with Madagascar, while similar orbicular jasper occurs worldwide.
