igneous
Rhyolite
Rhyolite (High-silica volcanic rock)
Hardness: 6-7 (Mohs); Color: Pink to reddish-brown with grey inclusions; Luster: Dull to earthy; Structure: Aphanitic to porphyritic (fine-grained matrix with some visible crystals); Specific Gravity: 2.4-2.6
- Hardness
- 6-7 (Mohs)
- Color
- Pink to reddish-brown with grey inclusions
- Luster
- Dull to earthy
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Physical properties
Hardness: 6-7 (Mohs); Color: Pink to reddish-brown with grey inclusions; Luster: Dull to earthy; Structure: Aphanitic to porphyritic (fine-grained matrix with some visible crystals); Specific Gravity: 2.4-2.6
Formation & geological history
Formed from the rapid cooling of silica-rich (felsic) magma/lava at or near the Earth's surface. Often resulting from explosive volcanic eruptions during the Cenozoic era or older volcanic episodes.
Uses & applications
Used primarily as crushed stone in construction, road fill, and sometimes as a decorative rock in landscaping or as a gemstone if it contains unique patterns like 'bird's eye' or jasper-like textures.
Geological facts
Rhyolite is the volcanic equivalent of granite; they have the same chemical composition but different cooling rates. Because of its high silica content, rhyolite lava is extremely viscous and can flow like cool molasses.
Field identification & locations
Identify in the field by its light color (pink/red), fine-grained texture, and extreme hardness (will scratch glass). Commonly found in volcanic mountain ranges and continental interior volcanic fields.
