sedimentary

Polished ocean jasper / orbicular jasper

Silicified rhyolite or chalcedony-rich microcrystalline quartz (SiO₂), commonly sold as ocean jasper

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; opaque to slightly translucent, tan, olive, cream, and brown with brecciated or orbicular patterns; waxy to vitreous luster and no visible cleavage. The rounded form is tumbled and polished, so natural crystal structure is microscopic.

Identified August 29, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed when silica-rich volcanic material and cavities were replaced or filled by chalcedony, quartz, and iron-bearing minerals, likely during Mesozoic volcanic activity. The distinctive Madagascar material is associated with altered rhyolitic flows.

Uses & applications

Used for cabochons, beads, carvings, polished stones, and decorative objects; valued mainly as an attractive lapidary material.

Geological facts

“Ocean jasper” is a trade name rather than a single rigorously defined mineral species; its circular patterns may be orbicular, brecciated, or plume-like depending on the deposit.

Field identification & locations

Identify it by its multicolored opaque chalcedony, fine patterns, high polish, and glass-scratching hardness; true Madagascar ocean jasper is strongly associated with coastal deposits near Marovato. A tumbled piece typically sells for about $5–$25, while exceptional patterned slabs or cabochons may reach $50–$200.