metamorphic
Polished orbicular jasper
Orbicular jasper (microcrystalline quartz/chalcedony, SiO₂, with iron-rich inclusions)
AI-generated identification · may be incorrectTypically hardness 6.5–7, opaque, with a waxy to vitreous polish and gray, black, white, or reddish spherical orbicules. It has no visible cleavage and a dense, cryptocrystalline structure; specific gravity is about 2.6.
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Physical properties
Typically hardness 6.5–7, opaque, with a waxy to vitreous polish and gray, black, white, or reddish spherical orbicules. It has no visible cleavage and a dense, cryptocrystalline structure; specific gravity is about 2.6.
Formation & geological history
Forms when silica-rich volcanic or hydrothermal material is altered and filled with concentric mineral aggregates, commonly involving chalcedony, quartz, feldspar, and iron oxides. Precise age depends on locality, with examples ranging from Precambrian to younger volcanic terrains.
Uses & applications
Used for cabochons, carvings, polished palm stones, beads, and decorative objects; it is not generally used as a major construction stone.
Geological facts
The rounded “orbicules” are diagnostic but can resemble leopard-skin rhyolite or orbicular granite. Polish can reveal patterns hidden on a weathered surface.
Field identification & locations
Identify it by its hard, glass-scratching surface, opaque silica-rich body, and repeated rounded spots or patches. Common sources include Madagascar, Mexico, Australia, Indonesia, and the western United States.
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