igneous
Rhyolite Pebble
Rhyolite
Hardness: 6-7 (Mohs scale); Color: Grayish-pink to reddish-tan; Luster: Dull/Earthy; Crystal Structure: Aphanitic (fine-grained matrix); Cleavage: None/Irregular fracture; Specific Gravity: 2.4-2.6
- Hardness
- 6-7 (Mohs scale)
- Color
- Grayish-pink to reddish-tan
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Grayish-pink to reddish-tan; Luster: Dull/Earthy; Crystal Structure: Aphanitic (fine-grained matrix); Cleavage: None/Irregular fracture; Specific Gravity: 2.4-2.6
Formation & geological history
Formed through the rapid cooling of silica-rich (felsic) lava at or near the Earth's surface. This specific specimen has been smoothed by water erosion, likely in a river or coastal environment.
Uses & applications
Commonly used as crushed stone for construction, road base, and landscape decoration. Polished pebbles are sometimes used in hobbyist jewelry or aquarium decor.
Geological facts
Rhyolite has the same chemical composition as granite but cooled much faster, preventing large crystals from forming. Its high silica content makes the lava very viscous and prone to explosive eruptions.
Field identification & locations
Identify in the field by its fine-grained texture, light color (felsic), and its inability to be scratched by a steel knife. It is common in volcanic regions like the American West or Iceland.
