DACITE (from Dacia, mod. Transylvania), in petrology, volcanic rocks which may be considered a quartz-bearing variety of andesite. Like the latter they consist for the most part of plagioclase felspar with biotite, hornblende, augite or enstatite, and have generally a porphyritic structure, but they contain also quartz as rounded, corroded phenocrysts, or as an element of the ground-mass. Their felspar ranges from oligoclase to andesite and labradorite ; sanidine occurs also in some dacites, and when abun dant gives rise to rocks which form transitions to the rhyolites. From this list of minerals it is readily seen that the dacites are the volcanic equivalent of the plutonic tonalites. Many of the horn blende- and biotite-dacites are grey or pale brown and yellow rocks with white f elspars and black crystals of biotite and hornblende; others, especially augite- and enstatite-dacites, are darker coloured. The rocks of this group occur in Hungary, Almeria (Spain), Argyllshire and other parts of Scotland, Victoria, New Zealand, the Andes, Martinique, Nevada and other districts of western North America, Greece, etc. They are mostly associated with andesites and trachytes, and form lava flows, dikes and in some cases massive intrusions in the centres of old volcanoes. Among continental petrographers the older dacites (Carboniferous, etc.) are often known as "porphyrites."