Chemical analyses of the most abundant components in rocks usually are presented as oxides of the elements; igneous rocks typically consist of approximately 12 major oxides totaling over 99 percent of the rock. It is contrasted with mafic rocks, which are relatively richer in magnesium and iron.Felsic refers to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, … Most syenitic seem to be associated with extensional tectonic regime (rifting continents). It is perhaps inevitable because minerals are something we can determine, unlike genesis which in many cases is still a mystery. The classification principles are shown on the diagram below. Compilations of many rock analyses show that rhyolite and granite are felsic, with an average silica content of about 72 percent; syenite, diorite, and monzonite… Mineralized smoky quartz veins and Phenocrysts that make up porphyry should be felsic (quartz, feldspar). The mafic syenite contains 50–70% alkali feldspar, while the leucocratic syenite is more uniform with about 85% feldspar. Typical accessory minerals are … 27 26 Mafic intrusive rocksi, mafic dikes and mafic sills 26a Molson mafic dike swarm (circa 1889 to 1871 Ma) and mafic … Carbonatite-alkalic intrusive suite (circa 1.8 to 1.9 Ga): carbonatite complexes, nepheline syenite, alkalic syenite, ijolite, fenite; associated mafic and ultramafic rocks . Alkali syenites may contain somewhat unusual minerals like aegirine, arfvedsonite, etc. The volcanic equivalent of syenite is trachyte. While the classification of plutonic rocks is based on mineralogical composition, the same approach is not practical with fine-grained or even partially glassy volcanic rocks. The influence of silica content on the particular minerals that crystallize from a rock magma is a complex interaction of several parameters, and it cannot be assumed that rocks with the same silica content will have the same mineralogy. Syenite is an igneous rock that solidified slowly in the crust in a similar manner to granite. The true syenites are rocks that fit into the area annotated in red. Mafic rocks derive from basalt protoliths and some volcanogenic sediments…, …the following groups: silicic or felsic (or acid, an old and discredited but unfortunately entrenched term), rocks having more than 66 percent silica; intermediate, rocks with 55 to 66 percent silica; and subsilicic, rocks containing less than 55 percent silica. (metagabbro, metadiorite and metagranite), and associated felsic (mafic syenite, porphyritic alkali syenite, quartz syenite) to mafic-ultramafic (chlorite-serpintinite-talc schist and undifferentiated ultramafics, birbirite) intrusions (Fig. ... Mount Vesuvius, in chlorite and talc schist in the Urals and Switzerland, and as an accessory mineral in alkaline and mafic igneous rocks, nepheline syenite, melilitite, kimberlites and rare carbonatites. Rocks like nepheline or sodalite syenites are actually curiosities that please the eye of a geologist, but are by no means common rocks we are likely to see all around us. The quartz syenite is grey, medium to coarse grain and massive, which was intruded by several felsic dikes observed in the field (Fig. Many so-called syenites are actually monzonites. Subsequently, one may also ask, is granite mafic felsic or intermediate? Actually, this is not true. Augite syenite forms their own dykes carrying blocks of source diorite. Click to see full answer. Nepheline syenite. At least some of them are believed to be fractionation products of alkali-rich basaltic magmas, but there are several different mechanisms responsible for the genesis of a syenitic magma. The mafic rock forms the outer part of the complex, while the leucocratic rock has a main central outcrop and a long, thin outcrop near the western margin of the complex (thought by van Breemen and his colleagues to be a ‘tail’ to the main crop folded round in D 2 ). Felsic and mafic rocks, division of igneous rocks on the basis of their silica content. Just so, is Granite felsic or mafic? It exhibits a characteristic schiller, but larvikite contains more plagioclase than alkali feldspar and is therefore monzonite. The fine-grained or glassy nature of many volcanic rocks makes a chemical classification such as the felsic-mafic taxonomy very useful in distinguishing the different types. Omissions? Felsic rocks can be produced by metamorphism of both igneous and sedimentary protoliths (e.g., granite and arkose, respectively) and are rich in silicon, sodium (Na), potassium, calcium, aluminum, and lesser amounts of iron and magnesium. 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