pantellerite

(from the article `rhyolite`) ...or alkali amphibole is the principal dark mineral, oligoclase will be rare or absent, and the feldspar phenocrysts will consist largely or ...
Found on http://www.britannica.com/eb/a-z/p/13

Pantellerite

Pantellerite is a peralkaline rhyolite. It has a higher iron and lower aluminium composition than comendite. It is named after Pantelleria, a volcanic island in the Strait of Sicily and the type location for this rock. On Pantelleria the rock is usually found as a vitrophyre containing phenocrysts of anorthoclase or sanidine. Quartz is found only ...
Found on http://en.wikipedia.org/wiki/Pantellerite
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