syenite

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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 It might be outdated or ideologically biased.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 ?
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.
Chaudhry, M.N., Ashraf, M., Hussain, S.S., 1981.Petrology of Koga nephiline syenites and pegmatites of Swat district.
Nepheline in a mesocratic syenite at Lac Rouge, Quebec (locality 76) is replaced by cancrinite and sodalite, which are subsequently altered to natrolite and thomsonite (Corriveau, 1984).
Beginning in late September 2003 and culminating in August 2004, the brothers labored long and expertly to penetrate, first, deep snow and ice cover and, next, a serious thickness of Giuv syenite, eventually to open a 50 cm X 2 meter X 6-meter cleft which produced smoky quartz crystal matrix plates to 80 cm long, with individual crystals to 25 cm, plus a few magnificent, medium-smoky open gwindels.
These are related to small but widely distributed Mesozoic alkaline rocks (granites and syenites) within a west-southwest to east-northeast trending belt (partially Taca-Taca, Rangel, Castro Tolay, Fundiciones, Hornillos bodies).
The constituent rocks majorly include alkali granites, syenites, nepheline syenites, carbonatites and albitites, all known as the major producers for REE bearing deposits.
Each augite had syenites. Anorthoclase-hornblende-augite-syenites, How many were going to St.
Cartwright, I., and Weaver, T.R., 1993, Fluid-rock interaction between syenites and marbles at Stephen Cross Quarry, Quebec, Canada: petrological and stable isotope data: Contributions to Mineralogy and Petrology, v.
The best color is therefore connected to the localities where veins are found within syenites. It is [.sup.40.K], a natural radioactive isotope, which causes the coloration of the quartz.
[3] However, whereas the trace element patterns of the Ambela granites and the syenites are characterised by a general negative Nb anomaly (particularly pronounced in the latter) and significantly spiked Rb-Ce segment, those of the inclusions are characterised by a positive Nb anomaly and a flat Rb-Ce segment.