igneous
Tumbled jasper or rhyolitic porphyry
Silicic volcanic rock, likely rhyolite (quartz- and feldspar-rich), possibly jasperized
AI-generated identification · may be incorrectSmall rounded tan-brown specimen with mottled pink, cream, and darker patches and a dull to slightly waxy luster; apparent hardness about 6–7 Mohs, opaque, with no visible cleavage. The pattern suggests a fine-grained volcanic matrix containing lighter feldspar/quartz areas, though the image is insufficient for exact i…
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Physical properties
Small rounded tan-brown specimen with mottled pink, cream, and darker patches and a dull to slightly waxy luster; apparent hardness about 6–7 Mohs, opaque, with no visible cleavage. The pattern suggests a fine-grained volcanic matrix containing lighter feldspar/quartz areas, though the image is insufficient for exact identification.
Formation & geological history
Likely formed from silica-rich volcanic lava or volcanic ash that cooled and later weathered and rounded; such rocks are commonly Cenozoic to Precambrian, depending on locality. If jasper, silica-rich fluids replaced or cemented the original rock after deposition.
Uses & applications
Used as a tumbled stone, lapidary material, ornamental aggregate, and inexpensive cabochon material; generally not used structurally in this small polished form.
Geological facts
Color and texture can overlap among jasper, rhyolite, welded tuff, and altered volcanic rocks. A streak test, hardness test, and close examination of grains are more diagnostic than color alone.
Field identification & locations
Common in volcanic terrains, especially the western United States, Mexico, Australia, and Madagascar. Identify with a hand lens: rhyolite shows fine groundmass and possible feldspar phenocrysts; jasper is typically uniformly microcrystalline and very opaque.
