igneous
Tumbled ocean jasper (orbicular jasper)
Silicified volcanic rhyolite; predominantly microcrystalline quartz/chalcedony with feldspar and iron-bearing minerals
AI-generated identification · may be incorrectHardness about 6.5–7 Mohs; opaque, gray-green, cream, pink, and reddish coloration with mottled or orbicular patterns; waxy to vitreous luster after polishing; no obvious cleavage; microcrystalline structure; specific gravity roughly 2.55–2.70.
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Physical properties
Hardness about 6.5–7 Mohs; opaque, gray-green, cream, pink, and reddish coloration with mottled or orbicular patterns; waxy to vitreous luster after polishing; no obvious cleavage; microcrystalline structure; specific gravity roughly 2.55–2.70.
Formation & geological history
Formed when silica-rich fluids replaced and cemented cavities or altered volcanic rhyolite, producing chalcedony and colorful mineral zones. Most commercial ocean jasper comes from Miocene-era volcanic rocks near Madagascar, approximately 5–23 million years old.
Uses & applications
Used for cabochons, beads, carvings, polished spheres, and collectible specimens; occasionally used as decorative stone. Its value is primarily ornamental rather than industrial.
Geological facts
The term “ocean jasper” is a trade name commonly applied to orbicular jasper from Madagascar; true orbicules may consist of concentric chalcedony, quartz, feldspar, or other alteration minerals.
Field identification & locations
Identify by its polished hardness, opaque silica-rich body, and irregular orbicular or brecciated patterns; it will not fizz in dilute acid and should scratch glass. Common sources include Madagascar, Indonesia, Mexico, and other volcanic regions.
