igneous
Rhyolite or jasper-bearing volcanic rock
Rhyolite, likely altered and silicified; red coloration may come from hematite
AI-generated identification · may be incorrectFine-grained, opaque, tan-brown and brick-red with earthy to dull luster; likely quartz- and feldspar-rich, with hematite/iron-oxide staining. Estimated hardness about 6–7 Mohs; cleavage is absent and fracture is irregular to conchoidal.
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Physical properties
Fine-grained, opaque, tan-brown and brick-red with earthy to dull luster; likely quartz- and feldspar-rich, with hematite/iron-oxide staining. Estimated hardness about 6–7 Mohs; cleavage is absent and fracture is irregular to conchoidal.
Formation & geological history
Formed from rapidly cooled, silica-rich volcanic lava, probably during a Cenozoic or older volcanic episode; later alteration and iron oxidation produced the red bands and mottling. Exact identification requires thin-section or chemical testing.
Uses & applications
Primarily a natural collectible or lapidary rough; attractive pieces may be cut or polished into cabochons. It has little commercial construction value in this small form.
Geological facts
The specimen’s contrasting red and tan zones resemble jasper, but visible granular texture and lack of translucency are consistent with altered rhyolite. Hematite commonly produces red, purple, and brown volcanic-rock colors.
Field identification & locations
Look for a hard, nonfoliated, very fine-grained matrix that scratches glass and commonly shows tiny quartz crystals or flow banding; a streak test and acid test are usually unhelpful. Similar material occurs in volcanic regions worldwide, including the western United States.
