syenite


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Related to syenite: trachyte

syenite

(sī`ənīt), coarse-grained igneous rockrock,
aggregation of solid matter composed of one or more of the minerals forming the earth's crust. The scientific study of rocks is called petrology. Rocks are commonly divided, according to their origin, into three major classes—igneous, sedimentary, and metamorphic.
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, similar in appearance and composition to granite. Unlike granite, it contains little or no quartz. The chief minerals in syenite are the feldspars, with mica, hornblende, and pyroxene. Varieties are distinguished (according to the ferromagnesian minerals contained) as augite syenite, hornblende syenite, mica syenite, and nepheline syenite. Syenites are comparatively rare rocks, being found chiefly in a few areas of the United States and Germany. They are occasionally substituted for granites as building stones.
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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Syenite

 

a holocrystalline plutonic rock composed chiefly of orthoclase and plagioclase, with admixtures of the following ferrous minerals: hornblende, biotite, pyroxene, and, occasionally olivine. Quartz is also sometimes present.

Depending on the content of ferrous minerals, syenite is classified as hornblende syenite, micaceous syenite, quartz syenite, and so forth. Syenite is characterized chemically by a silica content of 55 to 65 percent; the alkali content determines the classification of syenite into normal and alkali types. In normal syenites plagioclases are present as oligoclase and andesite. Alkali syenites contain orthoclase and, more rarely, albite. Nephelines or other feldspathoids, such as leucite and the so-dalite group of minerals, are formed when the alkali content exceeds 12 percent and the silica content is reduced; alkali syenites thus grade into nepheline syenites or other feldspathoid syenites. Monzonites or gabbro syenites are similar to syenites. They are composed of labradorite and orthoclase with admixtures of ferrous minerals, such as pyroxene.

In the USSR, syenites are abundant in the southern Ukraine (Volyn’ Oblast), the Urals, Kazakhstan, the Caucasus, and Middle Asia, where monzonites are found. Syenites are used for the same purposes as granites.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

syenite

[′sī·ə‚nīt]
(petrology)
A visibly crystalline plutonic rock with granular texture composed largely of alkali feldspar, with subordinate plagioclose and mafic minerals; the intrusive equivalent of trachyte.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
International in its scope, Unimin has established the quality standard for high purity quartz, and it is the world's primary supplier of nepheline syenite. Responding to the needs of our customers, we have also become a major producer of feldspar, dolomite, southern bentonite, ball clay, kaolin, and blended mineral products.
Occurrence: In a pegmatite in nepheline syenite. Associated minerals are: microcline, aegirine, arfvedsonite, nepheline, eudialyte, albite, lorenzenite, loparite, aenigmatite, manganneptunite, murmanite, analcime, natrolite, stilbite, chabazite, kuzmenkoite-Mn, nontronite, and others.
This morning, when Conrad Berther had first exposed the front part of the cleft, he appraised the syenite and the course of the veins of aplite and quartz.
Carbonitite, barytes, antimony and lead-antimony deposits in Chitral and nephlene syenite reserves in Swat will be developed in 1991-92.
+++ Nepheline syenite is not a true feldspar and is classified as afeldpathoid mineral.
The Ambela complex was considered to be late Paleozoic on the basis of whole-rock Rb-Sr (297 + 4, 315 + 15) and U-Pb zircon (280 + 15) ages from the Koga syenite (Le Bas et al., 1987 and Smith et al., 1994 respectively) and the intrusive contact of the Ambela granites with Carboniferous rock of the Jaffar Kandao Formation, where the Chinglai gneiss was also considered Carboniferous in age.
Malignite: A mafic nepheline syenite which has more than 5% nepheline and roughly equal amounts of pyroxene and potassium feldspar.
Here, results of phase space investigations for seismicity of natural and mining induced origin are presented: caused by San Andreas fault (California, USA) and Yake-dake volcano activity (Honshu, Japan) as well as generated by Katowice Coal Mine (Silesia, Poland) and seismoacoustic emission of syenite rock sample recorded during uniaxial compression test (conducted in Poland).
Table 1: South African Minerals Production, 1991 (t except where shown otherwise) Product Volume Gold 597.7 PGMs 62.6 Silver 170.7 Diamonds ('000ct) 8,446 Iron ore ('000t) 28,952 Manganese ore ('000t) 3,191 Chrome ore ('000t) 4,511 Cobalt 102 Copper 184,552 Nickel 11,568 Tin 1,042 Lead 74,971 Zinc 66,599 Coal: Bituminous ('000t) 174,995 Anthracite ('000t) 2,452 Uranium oxide 1,974 Andalusite 207,137 Asbestos 148,962 Fluorspar 270,341 Gypsum 431,482 Limestone/dolomite ('000t) 19,971 Magnesite 92,634 Nepheline syenite 20,966 Salt 685,597 Silica ('000t) 2,163 Sulphur (all forms) 516,958 Talc 8,235 Vermiculite 214,656 Technological change