igneous
Banded Rhyolite
Rhyolite (felsic volcanic rock)
Hardness: 6-7 (Mohs). Color: Light gray, buff, or tan with dark gray or black bands. Luster: Dull to vitreous. Crystal structure: Aphanitic (fine-grained) with flow banding. Cleavage: None. Specific gravity: 2.4-2.6.
- Hardness
- 6-7 (Mohs)
- Color
- Light gray, buff, or tan with dark gray or black bands
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 (Mohs). Color: Light gray, buff, or tan with dark gray or black bands. Luster: Dull to vitreous. Crystal structure: Aphanitic (fine-grained) with flow banding. Cleavage: None. Specific gravity: 2.4-2.6.
Formation & geological history
Formed from viscous, silica-rich volcanic lava that cooled rapidly on or near the Earth's surface. The distinct bands are caused by laminar flow of the lava during eruption and crystallization.
Uses & applications
Used primarily as decorative stone, in lapidary work for making cabochons, and sometimes as crushed stone in construction or road building.
Geological facts
Flow banding in rhyolite is a classic example of liquid movement preserved in stone; the bands represent layers of high and low viscosity that were stretched during the eruption.
Field identification & locations
Identify by crisp, fine-grained parallel or wavy bands and high silica content (scratching glass). Common in volcanic fields such as those in the Western United States (Utah, Nevada).
