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.

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.

References in periodicals archive ?
This is particularly interesting because unpublished information for an archaeolgical site that has no associated dacite bedrock indicates that the dacite came from the largest bedrock source site at Cache Creek--transported hundreds of kilometres some 2,000 to 6,000 years ago
No cross-cutting relationships were observed between the hornblende dacite porphyry (Fig.
La partie superieure de la Formation de Porten Road comporte une sequence interstratifree de rhyolite riche en quartz et de dacite pauvre en quartz provenant vraisemblablement de la fusion de Ia croute continentale.
The Ingalls Head Formation consists of grey to purple tuff, minor andesite to dacite flows, and grey to purple mudstone and sandstone.
Towards the base of the antimony zone, vein densities increase and the volcaniclastic andesite is intruded by dacite breccia with a narrow zone of gold mineralization from -395 to -405 feet.
The geologically-modelled strike extensions of both the C-1 and C-2 vein systems are covered by a 10-30m thick blanket of dacite tuff both to the east and west of the previously-drilled outcropping vein segments;
The volcanic country rock is composed of andesite with lesser rhyolite and dacite flows and dikes.
The area is characterized by post-mineral colluvium and gravel cover that obscures the underlying bedrock, but occurs immediately west of, and on the margins of, a small hill where a dacite dome sub-crops.
These vein systems occur within a vitreous rhyolite - dacite volcanic unit which has been altered and exhibits quartz-carbonate stockwork throughout the areas occupied by the veins.
The mineralized body is defined as a nearly flat lying 22 meter thick body of pyritized and silicified breccias in dacite following a low angle fault zone.
The East Zone consists of two sub-parallel, sub-vertical dipping hydrothermal breccias developed within a tuffaceous dacite and has been outlined over a strike length in excess of 400 metres and a maximum width of approximately 225 metres.