igneous
Rhyolite
Rhyolite (felsic extrusive igneous rock)
Hardness: 6-7 (Mohs); Color: Pink, light gray, or reddish-brown; Luster: Dull to earthy; Structure: Aphanitic to porphyritic; Specific Gravity: 2.4-2.6
- Hardness
- 6-7 (Mohs)
- Color
- Pink, light gray, or reddish-brown
- Luster
- Dull to earthy
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Physical properties
Hardness: 6-7 (Mohs); Color: Pink, light gray, or reddish-brown; Luster: Dull to earthy; Structure: Aphanitic to porphyritic; Specific Gravity: 2.4-2.6
Formation & geological history
Formed from the rapid cooling of silica-rich (felsic) lava at or near the Earth's surface. These lavas are highly viscous and typically associated with continental volcanic activity.
Uses & applications
Used primarily as crushed stone or aggregate for construction and road surfacing. Some decorative varieties like 'Bird's Eye Rhyolite' are used for lapidary work and jewelry.
Geological facts
Rhyolite has the same chemical composition as granite but cooled much faster, resulting in small crystals. It is often found in association with explosive volcanic eruptions due to its high gas content and viscosity.
Field identification & locations
Look for a fine-grained, light-colored rock with occasional visible quartz or feldspar phenocrysts. It often shows flow banding. Commonly found in tectonic areas like the Rocky Mountains and the Andes.
