igneous
Dalmatian jasper
Orbicular rhyolite, commonly sold as Dalmatian jasper; mainly quartz, feldspar, and altered mafic minerals
AI-generated identification · may be incorrectTypically cream to pale gray with black rounded spots, opaque, and fine-grained with a matte to lightly polished luster. Hardness is about 6–7 Mohs; cleavage is absent or poor and specific gravity is roughly 2.5–2.7.
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Physical properties
Typically cream to pale gray with black rounded spots, opaque, and fine-grained with a matte to lightly polished luster. Hardness is about 6–7 Mohs; cleavage is absent or poor and specific gravity is roughly 2.5–2.7.
Formation & geological history
Formed from silica-rich volcanic lava that cooled into rhyolite, with dark iron- and manganese-rich inclusions producing the spots. It is generally associated with relatively young volcanic provinces, especially Oligocene–Miocene material from Mexico.
Uses & applications
Used for cabochons, beads, carvings, polished stones, and decorative objects; it has modest value as an ornamental stone rather than as a fine gemstone.
Geological facts
The name “jasper” is a trade term here; much Dalmatian jasper is geologically rhyolite rather than true microcrystalline quartz jasper. Spot patterns vary substantially between pieces.
Field identification & locations
Identify it by its cream background, irregular black or brown spots, opaque volcanic texture, and lack of banding or obvious crystals; it should not fizz with dilute acid. Common commercial material comes from Mexico.
