sedimentary

Orbicular jasper (likely ocean jasper)

Silica-rich chert/jasper, primarily microcrystalline quartz (SiO₂)

AI-generated identification · may be incorrect

Typically gray-blue to brown with rounded cream, white, and reddish orbicules; opaque, waxy to dull luster, conchoidal fracture, no cleavage, and hardness about 6.5–7 Mohs. The visible rusty brown rim may reflect iron-oxide staining or weathered matrix.

Identified August 21, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich fluids replace or cement volcanic ash, sediment, or altered rock, producing concentric orbicules; many Madagascar ocean jaspers formed in Permian–Triassic volcanic environments roughly 250–300 million years ago. Exact locality cannot be confirmed from the image.

Uses & applications

Used for cabochons, beads, carvings, polished slabs, and decorative objects; large pieces are occasionally used as ornamental stone.

Geological facts

Orbicular patterns are diagnostic but not always true “ocean jasper”; similar orbicular jasper and rhyolite occur worldwide.

Field identification & locations

Identify by testing for glass-like hardness, absence of cleavage, opaque silica-rich texture, and contrasting spherical inclusions; common sources include Madagascar, Mexico, Oregon, and Australia. Avoid acid tests, which are generally uninformative.