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Syenite is a coarse-grained intrusive igneous rock with a general composition similar to that of granite, but deficient in quartz, which, if present at all, occurs in relatively small concentrations (< 5%).
Nepheline syenite is a holocrystalline plutonic rock that consists largely of nepheline and alkali feldspar. [1] The rocks are mostly pale colored, grey or pink, and in general appearance they are not unlike granites , but dark green varieties are also known.
The outermost layer, the Outer Coarse Syenite, encircles the entire Red Hill and is separated from the country rock by a zone of breccia composed of both the country rock and the Outer Coarse Syenite rock. [2] The Outer Coarse Syenite is composed of 10-20% mafic minerals and 80-90% perthitic feldspar.
The following is a list of rock types recognized by geologists.There is no agreed number of specific types of rock. Any unique combination of chemical composition, mineralogy, grain size, texture, or other distinguishing characteristics can describe a rock type.
A notable exception where feldspathoids and quartz-bearing rocks are found together is the Red Hill Syenite. [1] Foid, a contraction of the term feldspathoid, is applied to any igneous rock containing up to 60% modal feldspathoid minerals.
Nephelinite is a rock-forming mineral found in silica-poor igneous rocks. These include nepheline syenite, foidite, and phonolite. It is often found along with leucite, sodalite, potassium feldspars, and sodium-rich plagioclase, amphiboles, or pyroxenes, but almost never in association with quartz. [9]
Litchfieldite (nepheline syenite gneiss) from Canaã Massif, Brazil. Litchfieldite is a rare igneous rock.It is a coarse-grained, foliated variety of nepheline syenite, [1] sometimes called nepheline syenite gneiss or gneissic nepeheline syenite. [2]
The Concord Gabbro-Syenite Complex is a part of a larger suite of twenty plutons that form a chain extending almost 500 km, which lie within the Charlotte Metamorphic belt. [2] The complex is located in Cabarrus County in south central North Carolina .