igneous

Rhyolite

Rhyolite (felsic extrusive igneous rock)

Hardness: 6-7 (Mohs); Color: Pink, light gray, or reddish-brown; Luster: Dull to earthy; Structure: Aphanitic to porphyritic; Specific Gravity: 2.4-2.6

Hardness: 6-7 (Mohs)
Color: Pink, light gray, or reddish-brown
Luster: Dull to earthy

Identified May 23, 2026More igneous →

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Physical properties

Hardness: 6-7 (Mohs); Color: Pink, light gray, or reddish-brown; Luster: Dull to earthy; Structure: Aphanitic 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. These lavas are highly viscous and typically associated with continental volcanic activity.

Uses & applications

Used primarily as crushed stone or aggregate for construction and road surfacing. Some decorative varieties like 'Bird's Eye Rhyolite' are used for lapidary work and jewelry.

Geological facts

Rhyolite has the same chemical composition as granite but cooled much faster, resulting in small crystals. It is often found in association with explosive volcanic eruptions due to its high gas content and viscosity.

Field identification & locations

Look for a fine-grained, light-colored rock with occasional visible quartz or feldspar phenocrysts. It often shows flow banding. Commonly found in tectonic areas like the Rocky Mountains and the Andes.

Other igneous specimens

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

mineral

Dark Igneous Rock (Likely Basalt or Diabase)

Basalt (extrusive igneous rock) or Diabase (intrusive igneous rock - also known as Dolerite), largely composed of plagioclase feldspar, pyroxene (augite), and sometimes olivine and amphibole. Exact mineralogy would require thin section analysis.

Igneous