Les roches rhyolitiques permiennes à l'Ouest et au Nord-Ouest du Donon (Vosges septentrionales)

Two kinds of rhyolite outcrop N and NW of the Donon (Northern Vosges mountains). The most spread kind is sheet shaped. This phenocryst poor rock has a high MgO grade. It must be linked to the ignimbrites. The badly welded particles allowing an easy circulation of fumaroles are replaced by a micropoikilitic mass of quartz and feldspar. The second kind — Blancrupt's rhyolite — is dome shaped. It is a potassic rhyolite and seems to be a microgranite owing to the great amount of phenocrysts.