Rhyolite

Physical Properties

Hardness: 6-7 (Mohs scale), Color: Pinkish-red to grey/brown, Luster: Dull or sub-glassy, Crystal structure: Aphanitic (fine-grained) to porphyritic, 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. This specimen likely contains hematite inclusions giving it its reddish hue.

Uses & Applications

Used primarily in construction for crushed stone and road aggregate; occasionally used for decorative stone if it exhibits unique patterns like bird's eye or orbicular structures.

Geological Facts

Rhyolite is the volcanic equivalent of granite. Because of its high silica content, rhyolitic lava is very viscous (thick) and often erupts explosively rather than flowing easily like basalt.

Field Identification & Locations

Identify in the field by its fine-grained texture, light coloring (felsic), and the presence of small phenocrysts (visible crystals) of quartz or feldspar set in a dominant groundmass. Found globally in continental volcanic arcs.

Identified on: 4/29/2026

Mode: Standard