igneous
Vesicular Rhyolite with inclusions
Felsic extrusive igneous rock (Rhyolite)
Hardness: 6-7 (Mohs scale), Color: light gray to tan with black phenocrysts (likely Biotite or Hornblende), Luster: dull to earthy matrix with vitreous inclusions, Structure: vesicular/porous, Cleavage: none (conchoidal fracture), Specific Gravity: 2.4-2.6
Identified More igneous →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6-7 (Mohs scale), Color: light gray to tan with black phenocrysts (likely Biotite or Hornblende), Luster: dull to earthy matrix with vitreous inclusions, Structure: vesicular/porous, Cleavage: none (conchoidal fracture), 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. The small holes (vesicles) are created by gas bubbles trapped in the cooling magma.
Uses & applications
Used primarily in construction as crushed stone or decorative landscaping. Occasionally used as an abrasive or in lightweight concrete manufacturing.
Geological facts
Rhyolite is the volcanic equivalent of granite. If the same lava cooled underground slowly, it would have formed large-crystal granite instead of this fine-grained, porous rock.
Field identification & locations
Identify by its light color (indicating high silica), lightweight feel due to vesicles, and small visible crystals embedded in a fine-grained matrix. Commonly found in volcanic regions such as the Western US or Andes Mountains.
