metamorphic
Orbicular jasper (likely ocean jasper)
Silica-rich jasper, predominantly microcrystalline quartz (SiO₂), with iron-oxide and volcanic/mineral inclusions
AI-generated identification · may be incorrectMohs hardness about 6.5–7; opaque gray, cream, brown, and black orbicular pattern; vitreous to waxy luster; cryptocrystalline quartz with no cleavage; specific gravity roughly 2.5–2.7.
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Physical properties
Mohs hardness about 6.5–7; opaque gray, cream, brown, and black orbicular pattern; vitreous to waxy luster; cryptocrystalline quartz with no cleavage; specific gravity roughly 2.5–2.7.
Formation & geological history
Forms when silica-rich volcanic fluids fill cavities or replace volcanic rock, producing concentric mineral spherules; Madagascar ocean jasper is commonly Miocene–Pliocene in age. The polished, rounded specimen is human-processed.
Uses & applications
Used for cabochons, beads, carvings, ornaments, and lapidary collections; not generally used as a structural stone.
Geological facts
The circular “eyes” result from orbicular growth of quartz, feldspar, chalcedony, and iron oxides around nucleation points. “Ocean jasper” is a trade name rather than a single formally defined mineral species.
Field identification & locations
Identify by its opaque silica-rich body, abundant concentric orbs, hardness, and lack of acid reaction; common sources include Madagascar, Mexico, Australia, and Oregon. A steel knife should not easily scratch it.
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