igneous
Vesicular Rhyolite
Rhyolite (High-silica volcanic rock)
Hardness: 6-7 (Mohs scale), Color: light grey to tan with small reddish/dark speckles, Luster: dull/earthy, Texture: vesicular (holes) and aphanitic (fine-grained matrix)
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Physical properties
Hardness: 6-7 (Mohs scale), Color: light grey to tan with small reddish/dark speckles, Luster: dull/earthy, Texture: vesicular (holes) and aphanitic (fine-grained matrix)
Formation & geological history
Formed from the rapid cooling of silica-rich (felsic) lava at or near the Earth's surface. The holes (vesicles) were created by gas bubbles trapped in the magma as it solidified. Typical of Cenozoic era volcanic activity.
Uses & applications
Used as decorative stone in landscaping, as an abrasive (if many vesicles are present, similar to pumice), or as construction aggregate. High silica content makes it durable.
Geological facts
Rhyolite is the volcanic equivalent of granite; it has the same chemical composition but cooled much faster. If lava of this composition cooled instantly without gas bubbles, it would form obsidian.
Field identification & locations
Identify in the field by its light color, high hardness (cannot be scratched by a steel nail), and the presence of small pits or gas bubbles. Commonly found in volcanic belts like the Western United States or Andes.
