Rhyolite

Physical Properties

Hardness: 6-7 on Mohs scale; Color: Pink, reddish-brown, or gray; Luster: Dull to sub-vitreous; Structure: Aphanitic (fine-grained) often with flow banding; Specific Gravity: 2.4-2.6

Formation & Geological History

Formed through the rapid cooling of silica-rich (felsic) magma on or near the Earth's surface during volcanic eruptions. It is the extrusive equivalent of granite.

Uses & Applications

Used as crushed stone for road construction, fill material, and occasionally as structural stone or in landscaping. Decorative varieties with flow banding are used for lapidary work.

Geological Facts

Rhyolite has the same chemical composition as granite but cooled much faster. High silica content makes rhyolitic lava very viscous, often leading to explosive eruptions.

Field Identification & Locations

Identify by its light color (pink/tan/grey), fine-grained texture, and characteristic 'flow bands' or wavy lines. Found in volcanic regions like the American West (Rocky Mountains).

Identified on: 5/2/2026

Mode: Standard