Rhyolite

Physical Properties

Hardness: 6-7 Mohs; Color: pink, reddish, or gray; Luster: dull to earthy; Crystal structure: aphanitic to porphyritic; Cleavage: none; Specific gravity: 2.4-2.6

Formation & Geological History

Formed by the rapid cooling of silica-rich (felsic) lava at or near the Earth's surface. High viscosity prevents large crystal growth, often leading to a fine-grained or glassy texture.

Uses & Applications

Used as crushed stone for road construction, fill material, and occasionally in landscaping or as a gemstone if it contains unique patterns like Jasper.

Geological Facts

Rhyolite is the volcanic equivalent of granite. Because of its high silica content, rhyolitic lava is very thick and can lead to explosive volcanic eruptions.

Field Identification & Locations

Identify by its fine-grained texture, light coloring, and presence of small phenocrysts (visible crystals) like quartz or feldspar. Commonly found in mountainous volcanic regions.

Identified on: 4/30/2026

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