igneous

Vesicular Rhyolite

Extrusive igneous rock (high-silica rhyolite)

Mohs hardness of 6-7, typically light-colored (tan, pink, or gray due to high silica), earthy to vitreous luster, fine-grained groundmass with visible gas bubbles (vesicles), specific gravity of 2.4-2.6.

Identified March 5, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of high-viscosity, silica-rich lava at or near the Earth's surface. The pits or holes (vesicles) are created by trapped gas bubbles that escape as the lava solidifies. It can range in age from very recent to hundreds of millions of years.

Uses & applications

Used as decorative stone in landscaping, as an abrasive in industrial settings, and as an aggregate in lightweight concrete construction.

Geological facts

Rhyolite is the volcanic equivalent of granite. It is so thick and sticky when it flows that it often traps gases, leading to the highly textured, bubbly surface seen in specimens like this.

Field identification & locations

Identify in the field by its light weight (due to vesicles), light color, and the presence of small holes. Commonly found in volcanic regions such as the American West, Iceland, and New Zealand.

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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

Magnetite

Iron(II,III) oxide (Fe3O4)

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Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

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Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

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Magnetite

Magnetite (Fe3O4)

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