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
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Physical properties
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.
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.
