mineral
Orbicular jasper (likely ocean jasper)
Silicified rhyolite/chert; chiefly microcrystalline quartz (SiO₂) with iron-oxide and clay-rich inclusions
AI-generated identification · may be incorrectHardness about 6.5–7 Mohs; opaque blue-gray with cream, tan, and rusty-orange veining or orbicular patches; dull to waxy luster and no visible cleavage. The irregular brecciated pattern suggests silica-filled fractures and altered volcanic material.
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Physical properties
Hardness about 6.5–7 Mohs; opaque blue-gray with cream, tan, and rusty-orange veining or orbicular patches; dull to waxy luster and no visible cleavage. The irregular brecciated pattern suggests silica-filled fractures and altered volcanic material.
Formation & geological history
Forms when silica-rich volcanic rock or volcanic ash is later replaced and cemented by chalcedony, quartz, and iron oxides; most ocean jasper is Oligocene–Miocene age volcanic material from Madagascar. Exact identification requires a fresh surface, hardness, and locality data.
Uses & applications
Used for cabochons, beads, carvings, polished slabs, and ornamental stone; rough pieces are mainly sold to collectors and lapidaries.
Geological facts
“Ocean jasper” is a trade name applied to patterned jasper, especially material from Madagascar; orbicular patterns are commonly produced by concentric silica and mineral alteration rather than true large crystals.
Field identification & locations
Check for a glass-scratching hardness, opaque microcrystalline texture, waxy fracture, and rusty iron staining; distinguish it from painted or resin-filled material with a loupe or fresh chip. Common sources include Madagascar, Oregon, Idaho, and Mexico.
