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Very fine crystalline or glassy rock of volcanic origin, composed chiefly of sodic plagioclase and free silica with subordinate dark-colored minerals.



a magmatic rock that is the effusive equivalent of granodiorite and quartz-diorite. Dacite consists of a finegrained or vitreous basic mass and phenocrysts of plagioclase and quartz, more rarely, of hornblende, biotite, and pyroxene, and sometimes, sanidine. Where albitization processes are widely developed, dacite turns into quartz al-bitophyre. Dacites were ejected by volcanoes in the Paleozoic (in the Urals, for example), Mesozoic, and Cenozoic (in the Caucasus, for example). They are also found among modern lavas on Kamchatka.

References in periodicals archive ?
Dacite porphyry containing abundant large quartz phenocrysts appears to be spatially associated with gold mineralization.
Different pyroclastic and volcanic products (acidic to intermediate composition) are exposed, but dacite predominates.
The volcanic rocks in the Tarom area vary from rhyodacite and dacite to basalt.
16 Ma) is a dacite, and the deeply weathered Mano de Pilon (undated) is either an andesite or dacite.
The main volcanic lithologies are predominately rhyolite, dacite and andesite of Eocene to Miocene in age.
Earlier work by Little River GoldFields NL attempted to identify the source of the gold in the Dalmorton goldfields as related to the nearby Dacite occurrences.
No doubt climatological conditions and the right vines matched to the right soil are important, but it is remarkable how well the block location corresponds to a dominant dacite unit lithology.
Semilir formation includes interbedded tuff breccias, pumize breccias, dacite tuff and andesite tuffs and tuffaceous claystone.
Dacite is typically aphanitic to weakly porphyritic, consisting mainly of plagioclase phenocrysts suspended in a plagioclase-rich groundmass with minor quartz.
Both the lower and upper volcanic assemblages are generally calc-alkaline and include units of basalt, andesite, dacite and rhyolite.
The Ruiz-Tolima complex was produced by repeated eruptions of andesite and dacite lavas and andesite pyroclastics.