igneous
Rhyolite
Rhyolite (High-silica volcanic rock)
Hardness: 6-7 (Mohs scale); Color: Gray, reddish-pink, or tan; Luster: Dull to vitreous; Crystal structure: Aphanitic (fine-grained) to porphyritic; Specific gravity: 2.4-2.6
- Hardness
- 6-7 (Mohs scale)
- Color
- Gray, reddish-pink, or tan
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Gray, reddish-pink, or tan; Luster: Dull to vitreous; Crystal structure: Aphanitic (fine-grained) to porphyritic; Specific gravity: 2.4-2.6
Formation & geological history
Formed through the rapid cooling of silica-rich (felsic) magma/lava at or near the Earth's surface. Common in volcanic arc and continental rift environments across various geological ages.
Uses & applications
Used primarily as crushed stone for road construction and concrete aggregate. Some decorative varieties like 'wonderstone' are used for carving or lapidary arts.
Geological facts
Rhyolite has the same chemical composition as granite but cooled much faster. If the magma cools almost instantly, it forms volcanic glass (obsidian) instead of rhyolite.
Field identification & locations
Identify by its light color and fine-grained texture; sometimes contains small visible crystals (phenocrysts). Common in the western United States and other volcanic regions.
