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(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.



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.


A visibly crystalline plutonic rock with granular texture composed largely of alkali feldspar, with subordinate plagioclose and mafic minerals; the intrusive equivalent of trachyte.
References in periodicals archive ?
Field relations of litchfieldite and soda syenites of Litchfield, Maine.
Continue to test for high grade mineralised structures located within the surrounding basalt, away from the syenites.
This paper encompasses the study on the preparation of industrial chemicals by acid leaching from the Koga nepheline syenite, Southern Swat, Lesser Himalayas-Pakistan.
Second, two of the four lithologies, the Ambela granites and the syenites are compared for Nb anomaly (Clause [3]).
In no part of this conglomerate have I ever seen pebbles of granite, syenite or the cristaline rocks although I have searched carefully for them for nearly two years, over the entire extent of the deposit, Had these rocks been on the surface at the time, the sedimentary deposits would certainly have abutted against them, instead of, as we find them, showing only their under surface in contact; and the presence of contained pebbles of granite etc, would have been inevitable.
The best color is therefore connected to the localities where veins are found within syenites.
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 Eddy property is underlain by mid Proterozoic sediments of the Purcell Supergroup that have been intruded by quartz diorites and monzonites of the mid-Cretaceous Bayonne plutonic suite and possibly by the Eocene Coryell syenites.