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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 ?
In summary of provenance indications, the Petit Anse-Gros Nez section, which forms the basal to central parts of the Horton Group, gives evidence of derivation from the northwest and from terranes dominated by slightly metamorphosed volcanic rocks, largely of dacitic composition, and lesser plagioclase-rich sandstone.
1980) recognized a unit of dacitic tufts and breccias (their 'Bluff tuff-breccia') overlain by andesitic sedimentary and tuffaceous rocks (the term 'possibly' is used here because descriptions of rock units by different authors are comparable only in a general sense, not in detail).
Ongoing core drilling of the Cieneguita mineralization system has confirmed that mineralization occurs mainly as disseminations hosted by dacitic tuffs and hydrothermal breccia bodies.
Geology, volcanology and petrology of Cerro Bravo, a young dacitic stratovolcano in West-central Colombia: Unpublished MSc thesis, Lousiana State Univ, 244 p.
The Priest Cove Formation includes coarse- to fine-grained mafic tuff, graded volcaniclastic sandstone and laminated siltstone, and minor dacitic crystal-lithic lapilli tuff(Fyffe and Grant 2001, 2003).
project, which is also hosted in a similar age dacitic complex, produced some
The Fourchu Group consists primarily of dacitic lapilli and ash turf and rare flows; basaltic, andesitic, and rhyolitic tuff and flows are minor components.
The Guazapares project is dominated by flows and tuffs of rhyolitic- dacitic and in lesser amount of andesitic composition that may correspond to the upper portion of the Lower Volcanic series of the Sierra Madre Occidental Volcanic Complex.
graphitic siltstone, shale and calcareous phyllite with dacitic intrusives and
All drill holes intersected well mineralized volcanic rocks, which have been intruded by swarms of dacitic dikes.
The volcanic rocks plot mainly in the rhyolitic and dacitic fields and one sample in the basaltic-andesitic field.
The Bayswater Formation comprises a sequence of rhyolitic to dacitic, lithic to lithic-crystal lapilli tuff and subordinate andesitic lithic tuff, thin-bedded tuffaceous siltstone and micaceous phyllite, and constitutes one of several steeply-dipping, northwest-younging volcanic sequences within the