Syenite is intrusive igneous rock that basically composed of an alkali feldspar and a ferromagnesian mineral. A unique group of alkali syenites is characterized by the presence of a feldspathoid mineral inclusive of nepheline, leucite, cancrinite, or sodalite (see nepheline syenite). Chemically, syenites comprise a slight amount of silica, incredibly big amounts of alkalies, and alumina.
Volcanic Equivalent: Trachyte
Texture: phaneritic (medium to coarse grained)
Colour: variable but typically light coloured.
Name origin: The name of syenite originally Syene that comes from in Egypt
Classification of Syenite
The classification on the QAPF diagram. Different syenitic rock types cover large part of the diagram. The true syenites are rocks that fit into the area annotated in red. Syenitic rocks are mostly composed of alkali feldspar (A) with minor amounts of quartz (Q). Plagioclase feldspar (P) is clearly less important than alkali deldspar. Foid syenites contain significant amount of relatively rare silicate minerals known as feldspathoids (F) which are called foids for simplicity. Note that Q and F are mutually exclusive. Syenitic rock that contains quartz can not contain feldspathoids and vice versa — foid-bearing and foid syenites contain no quartz.
Syenite Chemical Composition
Syenite predominant mineral is alkaline charecter. Plagioclase feldspar may be present small amaount less than 10%. Such feldspars often are interleaved as perthitic components of the rock. if ferromagnesian minerals are present in syenite most of all, they usually occur hornblende, amphibole and clinopyroxene. Biotite is rare. Other common accessory minerals are apatite, titanite, zircon and opaques.
Most syenites are either peralkaline with high proportions of alkali elements relative to aluminum, or peraluminous with a higher concentration of aluminum relative to alkali and earth-alkali elements (predominantly K, Na, Ca).
Formation of the Syenite
Formation of syenites are products of alkaline igneous activity, usually formed in thick continental crustal areas, or in Cordilleran subduction zones. Producing Syenite is necessary to melt a granitic or igneous protolith to a fairly low degree of partial melting. This is required because potassium is an incompatible element and tends to enter a melt first, whereas higher degrees of partial melting will liberate more calcium and sodium, which produce plagioclase, and hence a granite, adamellite or tonalite.
At very low degrees of partial melting a silica undersaturated melt is produced, forming a nepheline syenite, where orthoclase is replaced by a feldspathoid such as leucite, nepheline or analcime.
Conversely in certain conditions, large volumes of anorthite crystals may precipitate from thoroughly molten magma in a cumulate process as it cools. This leaves a drastically reduced concentration of silica in the remainder of the melt. The segregation of the silica from the melt leaves it in a state that may favour syenite formation.
Where is Syenite Located
Syenite is not a common rock. Regions where it occurs in significant quantities include the following.
In the Kola Peninsula of Russia two giant nepheline syenite bodies exists making up the Lovozero Massif and the Khibiny Mountains. These syenites are part of the Kola Alkaline Province.
In North America syenite occurs in Arkansas and Montana. Regions in New England have sizable amounts, and in New York syenite gneisses occur. The “great syenite dyke” extends from Hanging Rock, South Carolina through Taxahaw, South Carolina to the Brewer and Edgeworth mine in Chesterfield, South Carolina.Syenite clasts containing fluorescent sodalite were found on a beach in Michigan in 2017.
In Europe syenite may be found in parts of Switzerland, Germany, Norway, Portugal, in Plovdiv, Bulgaria and in Ditrău, Romania.
In Africa there are syenite formations in Aswan, Egypt, and in Malawi in the Mulanje Mountain Forest Reserve. Syenite rock was used to make the Quay with Sphinxes.
In Australia syenite occurs as small intrusive bodies in nearly every state. In New South Wales, a large syenite intruded during the breakup of Gondwana in the Cretaceous.
Uses of The Syenite Rock
- Flooring, Homes, Hotels, Interior Decoration
- As Building Stone, As Facing Stone, Paving Stone, Garden Decoration, Office Buildings
- As Dimension Stone, Cement Manufacture, Construction Aggregate, for Road Aggregate, Landscaping, Making natural cement, Manufacture of Magnesium and Dolomite Refractories
- Artifacts, Monuments, Sculpture, Small Figurines
- Cemetery Markers, Creating Artwork
Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
Wikipedia contributors. (2019, March 5). Syenite. In Wikipedia, The Free Encyclopedia. Retrieved 01:31, April 11, 2019, from https://en.wikipedia.org/w/index.php?title=Syenite&oldid=886262766