igneous
Rhyolite (likely porphyritic)
Rhyolite; chiefly quartz, alkali feldspar, plagioclase, and volcanic glass, with possible iron-oxide staining
AI-generated identification · may be incorrectLight gray to pink and greenish, fine-grained with a rough weathered surface and possible small phenocrysts; hardness about 6–7, generally vitreous to dull luster, no obvious cleavage as a whole, and specific gravity around 2.4–2.6.
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Physical properties
Light gray to pink and greenish, fine-grained with a rough weathered surface and possible small phenocrysts; hardness about 6–7, generally vitreous to dull luster, no obvious cleavage as a whole, and specific gravity around 2.4–2.6.
Formation & geological history
An extrusive felsic igneous rock formed when silica-rich lava cooled rapidly at or near Earth’s surface, commonly during volcanic eruptions from the Precambrian to Recent.
Uses & applications
Used as crushed aggregate, building stone, landscaping rock, and occasionally as a decorative or collectible specimen; typically not suitable for gemstones.
Geological facts
Rhyolite is the volcanic equivalent of granite and can display pink feldspar, quartz, and colorful alteration or oxidation patterns.
Field identification & locations
Common in volcanic regions such as Yellowstone, the western United States, Mexico, Iceland, and New Zealand. Field identification relies on its pale color, fine texture, high silica content, and lack of strong layering; a hand lens can reveal feldspar or quartz phenocrysts.
