This article needs additional citations for verification
. (September 2013)
A sample of rhyodacite from Slovakia
Rhyodacite is an extrusive volcanic rock intermediate in composition between dacite and rhyolite. It is the extrusive equivalent of granodiorite. Phenocrysts of sodium-rich plagioclase, sanidine, quartz, and biotite or hornblende are typically set in an aphanitic to glassy light to intermediate-colored matrix.
Rhyodacite is a high silica rock containing 20% to 60% quartz with the remaining constituents being mostly feldspar. The feldspar is a mix of alkaline feldspar and plagioclase, with plagioclase forming 35% to 65% of the mix. Rhyodacite often exists as explosive pyroclastic volcanic deposits.
Rhyodacite lava flows occur, for example, in northwestern Ferry County (Washington), and at An Sgùrr on the island of Eigg in Scotland.
||Wikimedia Commons has media related to Rhyodacite.
- ^ a b "Geologic units containing rhyodacite". usgs.gov.
- ^ Emeleus, C.H. and Bell, B.R. (2005) British Regional Geology: The Palaeogene Volcanic Districts of Scotland, 4th edition, Nottingham, British Geological Survey, page 77