igneous
Weathered rhyolite or felsic volcanic rock
Rhyolite, commonly quartz–alkali feldspar–plagioclase with iron-oxide alteration
AI-generated identification · may be incorrectFine-grained, pale gray to pink-red, dull to slightly earthy luster, with possible faint porphyritic texture; hardness roughly 6–7, no obvious cleavage, and specific gravity about 2.4–2.7. The red coloration likely comes from hematite or limonite staining.
Identified More igneous →
Explore Weathered rhyolite or felsic volcanic rock in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Fine-grained, pale gray to pink-red, dull to slightly earthy luster, with possible faint porphyritic texture; hardness roughly 6–7, no obvious cleavage, and specific gravity about 2.4–2.7. The red coloration likely comes from hematite or limonite staining.
Formation & geological history
An extrusive igneous rock formed when silica-rich lava cooled rapidly at or near Earth’s surface, generally in volcanic settings. Its exact geological age cannot be determined from the photograph; weathering and hydrothermal alteration have modified the surface.
Uses & applications
Used locally as crushed aggregate, road material, landscaping stone, and building stone; attractive polished pieces may be collected, though this specimen appears ordinary and heavily weathered.
Geological facts
Rhyolite is the volcanic equivalent of granite and can contain microscopic quartz and feldspar crystals. Red patches commonly reflect oxidation of iron-bearing minerals.
Field identification & locations
Identify it by its very fine grain, light felsic color, hardness, and absence of visible large crystals; a streak, hand lens, and acid test would help distinguish it from altered granite or volcanic tuff. Common in volcanic belts worldwide, including the western United States.
