igneous

Porphyritic Rhyolite

Rhyolite (Porphyry)

Hardness: 6-7 on Mohs scale. Color: Salmon pink to reddish-brown with light-colored phenocrysts. Luster: Dull/earthy matrix with vitreous crystals. Crystal structure: Aphanitic matrix with visible crystals. Cleavage: None. Specific gravity: 2.4-2.6.

Hardness: 6-7 on Mohs scale
Color: Salmon pink to reddish-brown with light-colored phenocrysts
Luster: Dull/earthy matrix with vitreous crystals

Identified May 26, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of silica-rich (felsic) lava at or near the Earth's surface. The larger crystals (phenocrysts) formed slowly underground before the final eruption. Common in volcanic regions of all geological ages.

Uses & applications

Used primarily as decorative stone, crushed aggregate for construction, and occasionally in jewelry as polished cabochons or river stones.

Geological facts

Rhyolite is the volcanic equivalent of granite. The name comes from the Greek word 'rhyax', meaning a stream of lava. Many 'wonderstone' specimens are forms of rhyolite.

Field identification & locations

Identify by the fine-grained 'sandy' looking matrix containing distinct, larger crystals of quartz or feldspar. Often found as water-worn pebbles in riverbeds or near volcanic arcs.

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