| Igneous rock | |
 | |
| Composition | |
|---|---|
| Classification | Felsic |
| Primary | Quartz and alkali feldspar (sanidine and sodic plagioclase) |
| Secondary | Biotite and hornblende |
| Texture | Glassy or aphanitic, sometimes porphyritic |
Rhyolite (/ˈraɪ.əlaɪt/ RY-ə-lyte)[1][2][3][4] is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral assemblage is predominantly quartz, sanidine, and plagioclase. It is the extrusive equivalent of granite.
Its high silica content makes rhyolitic magma extremely viscous. This favors explosive eruptions over effusive eruptions, so this type of magma is more often erupted as pyroclastic rock than as lava flows. Rhyolitic ash-flow tuffs are among the most voluminous of continental igneous rock formations.
Rhyolitic tuff has been used extensively for construction. Obsidian, which is rhyolitic volcanic glass, has been used for tools from prehistoric times to the present day because it can be shaped to an extremely sharp edge. Rhyolitic pumice finds use as an abrasive, in concrete, and as a soil amendment.
- ^ Wells, John C. (2008). Longman Pronunciation Dictionary (3rd ed.). Longman. ISBN 978-1-4058-8118-0.
- ^ "rhyolite". Dictionary.com Unabridged (Online). n.d.
- ^ "rhyolite". Merriam-Webster.com Dictionary. Merriam-Webster. Retrieved 2012-07-10.
- ^ "rhyolite". The American Heritage Dictionary of the English Language (5th ed.). HarperCollins.