metamorphic

Orbicular jasper (likely ocean jasper)

Silicified microcrystalline quartz/chalcedony with orbicular patterns; SiO₂

AI-generated identification · may be incorrect

Polished, dark brown chalcedony matrix containing cream-to-tan spherical orbicules; vitreous to waxy luster, cryptocrystalline structure, no visible cleavage, Mohs hardness about 6.5–7, specific gravity roughly 2.6.

Identified September 8, 2026More metamorphic →

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Physical properties

Formation & geological history

Forms when silica-rich volcanic material is altered and replaced by chalcedony, producing concentric orbicules; classic ocean jasper formed mainly in Miocene volcanic rocks of Madagascar, though similar orbicular jaspers occur elsewhere.

Uses & applications

Used for cabochons, beads, carvings, spheres, and ornamental objects; valued primarily as a decorative lapidary stone.

Geological facts

The orbicules may consist of concentric chalcedony, quartz, feldspar, and iron-oxide layers. “Ocean jasper” is a trade name often applied broadly to orbicular jasper.

Field identification & locations

Identify by its opaque brown groundmass, rounded cream spots, polish, and inability to scratch glass only weakly or not at all; confirm with a hardness test on an inconspicuous area. Common sources include Madagascar, Mexico, and Australia.