Dacite

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dacite

[′dā‚sīt]
(geology)
Very fine crystalline or glassy rock of volcanic origin, composed chiefly of sodic plagioclase and free silica with subordinate dark-colored minerals.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Dacite

 

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.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
The comparison of plagioclase factors with the other areas show that our results are meaningful and as a rule, the number of plagioclase nuclei is less than for amphibole in the dacitic rocks.
Dacitic lavas without disequilibrium features dominate the N3 group, being accompanied by some mixed lavas with similar chemical composition.
Chlorite mottled schist, in which most orebodies are found, is believed to be the schistose equivalent of dacitic tuff-breccias.
The dacitic lava flows generally occur as lava domes plugs and small satellite volcanoes inside and around Koh-e-Sultan Volcano.
As these clasts generally contain quartz, they can broadly be called dacitic. Many of these clasts are also clearly phyllitic with sericitic groundmass.
The lithology of the area consists of greenschists, mica schists, quartzites, hornblende schists, amphibolites, garnet-amphibolites, serpentinites and porphyritic hypabyssal rocks with andesitic to dacitic composition (Figure 1).
and Beni, E.: 2004, Morfological analysis of Nevado de Toluca volcano (Mexico): new insights into the structure and evolution of an andesitic to dacitic stratovolcano.
Younger dacitic volcanics and sandy conglomerates overlie the andesite / limestone sequence.
Felsic rocks range from dacitic to rhyolitic in composition, and normally contain quartz and plagioclase phenocrysts; felsic rocks are commonly coarsely fragmental and are characterized by a considerable array of fragment types and sizes within and among units, as well as by variable amounts of juvenile volcanic material in the matrix.
Occurrence: In highly altered andesitic to dacitic rocks.
The most advanced of Gabriel's projects is Rosia Montana, 85 km north of Deva, where a programme of underground channel sampling and surface diamond drilling has confirmed gold mineralisation associated with multiple fractures and brecciated zones within two dacitic intrusions, Cetate and Cirnic.