igneous
Banded Rhyolite (or Gray Shale pebble)
Rhyolite (SiO2 with minor impurities)
Hardness: 6-7 (Mohs scale), Color: light gray to blue-gray, Luster: dull to earthy, Crystal structure: aphanitic to porphyritic, Cleavage: none, Specific gravity: 2.4-2.6
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Physical properties
Hardness: 6-7 (Mohs scale), Color: light gray to blue-gray, Luster: dull to earthy, Crystal structure: aphanitic to porphyritic, Cleavage: none, Specific gravity: 2.4-2.6
Formation & geological history
Formed through the rapid cooling of silica-rich lava at or near the Earth's surface during volcanic eruptions. Most surface specimens are from the Cenozoic era.
Uses & applications
Used primarily as crushed stone for road construction, landscaping, and occasionally as decorative gravel or for tumbling by amateur collectors.
Geological facts
Rhyolite is the extrusive equivalent of granite; its rapid cooling prevents large crystal growth, resulting in its fine-grained texture.
Field identification & locations
Identify by its light color, fine-grained texture, and hardness (it will usually scratch glass). Commonly found in volcanic mountain ranges and volcanic island arcs.
