igneous
Polished ocean jasper or orbicular rhyolite
Silicified, spherulitic rhyolite; chiefly quartz, feldspar, and chalcedony
AI-generated identification · may be incorrectGreen-brown rounded polished stone with cream orbicules, opaque to slightly translucent areas, and a dull-to-waxy luster. Hardness is approximately 6.5–7 Mohs; cleavage is absent, with conchoidal fracture possible.
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Physical properties
Green-brown rounded polished stone with cream orbicules, opaque to slightly translucent areas, and a dull-to-waxy luster. Hardness is approximately 6.5–7 Mohs; cleavage is absent, with conchoidal fracture possible.
Formation & geological history
Likely volcanic rhyolite altered and partially silicified by circulating fluids, with orbicules formed during cooling or later mineral growth. Most ocean jasper comes from Miocene volcanic rocks of Madagascar, though visual identification from the image is not definitive.
Uses & applications
Used as a tumbled stone, cabochon, bead, and collector specimen; it has little industrial or construction use. Typical value is about $5–$25 for a small polished piece, or $30–$100+ for distinctive high-grade material.
Geological facts
The cream spots are commonly feldspar-, quartz-, or chalcedony-rich spherulites. “Ocean jasper” is a lapidary trade name rather than a single formally defined mineral species.
Field identification & locations
Look for rounded orbicules in a fine-grained volcanic matrix, very high scratch resistance, and no metallic streak; a glass or steel scratch test and magnification help distinguish it from resin or glass. Common sources include Madagascar, Mexico, and other rhyolitic volcanic terrains.
