igneous
Banded Rhyolite
Rhyolite (High-silica volcanic rock)
Hardness: 6-7 on Mohs scale. Color: Cream to light gray with darker gray/green mottled bands or spots. Luster: Dull to sub-vitreous. Crystal structure: Aphanitic (fine-grained) to porphyritic matrix. Specific gravity: 2.4-2.6.
- Hardness
- 6-7 on Mohs scale
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Cream to light gray with darker gray/green mottled bands or spots. Luster: Dull to sub-vitreous. Crystal structure: Aphanitic (fine-grained) to porphyritic matrix. 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. This specific water-worn specimen likely originated from volcanic flows that were later eroded and transported by water, rounding its edges.
Uses & applications
Used primarily as construction aggregate, road stone, and occasionally for decorative landscaping or as lapidary material for polishing into 'river stones'.
Geological facts
Rhyolite has the same chemical composition as granite but cooled much faster. Its high silica content makes the lava extremely viscous, often leading to explosive volcanic eruptions rather than smooth flows.
Field identification & locations
Identify in the field by its light color, high hardness (cannot be scratched by a steel knife), and fine-grained texture. Commonly found in volcanic arcs and continental crust regions. Collectors look for unique banding patterns or inclusions.
