2). Plagioclase may appear in syenitic rocks in addition to perthitic alkali feldspar also as a separate phase. Syenitic rocks are usually associated with other plutonic rocks. Our editors will review what you’ve submitted and determine whether to revise the article. Such feldspar intergrowth is named perthite and this is the reason why syenite is more common rock type than alkali feldspar syen. This broad grouping on the basis of mineralogy related to silica content is used in many modern classification schemes. Because of this abundance and because most igneous minerals are silicates, silica content was used as a basis of early classifications; it remains widely accepted today. For some reason the term “monzonite” seem to be little known and rarely used. Quartz alkali feldspar syenite from Estonia. In a widely accepted silica-content classification scheme, rocks with more than 65 percent silica are called felsic; those with between 55 and 65 percent silica are intermediate; those with between 45 and 55 percent silica are mafic; and those with less than 45 percent are ultramafic. The latter may be further divided into two groups: mafic,…, …or quartz, giving the term felsic; other felsic minerals are corundum, zircon, muscovite, lepidolite, and calcite. Larvikite is a famous decorative stone from Norway. Such feldspar intergrowth is named perthite and this is the reason why syenite is more common rock type than alkali feldspar syen. Just so, is Granite felsic or mafic? The mafic syenite contains 50–70% alkali feldspar, while the leucocratic syenite is more uniform with about 85% feldspar. This article was most recently revised and updated by, https://www.britannica.com/science/felsic-rock. The majority of rocks in this suite are metaluminous (Maniar and Piccoli, 1989) and type I (igneous origin; Chappell and White, 1974). Syenitic rock that contains quartz can not contain feldspathoids and vice versa — foid-bearing and foid syenites contain no quartz. Augite syenite forms their own dykes carrying blocks of source diorite. Granite is an extremely beautiful stone which has made its revival in regarding new houses today and also the remodeling of older houses. Carbonatite-alkalic intrusive suite (circa 1.8 to 1.9 Ga): carbonatite complexes, nepheline syenite, alkalic syenite, ijolite, fenite; associated mafic and ultramafic rocks . Other articles where Intermediate rock is discussed: felsic and mafic rocks: …and 65 percent silica are intermediate; those with between 45 and 55 percent silica are mafic; and those with less than 45 percent are ultramafic. The traditional Egyptians saw the good thing about granite and tried on the extender within their houses as flooring. Let us know if you have suggestions to improve this article (requires login). 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. Saw-cut profiles through pillow-syenite-gneiss sections have … Learn vocabulary, terms, and more with flashcards, games, and other study tools. Silica saturation is a classification of minerals and rocks as oversaturated, saturated, or undersaturated with respect to silica. They are classified according to their chemistry and the results are plotted on the TAS diagram. It is perhaps inevitable because minerals are something we can determine, unlike genesis which in many cases is still a mystery. The following lithologies were investigated: nordmarkite, larvikite, porphyritic syenite, microsyenite, mafic-felsic magma mingling in alkali ganite, and nepheline syenite. Felsic igneous rock and a type of granite rich in the mineral potassium feldspar . Ring in the new year with a Britannica Membership. Different syenitic rock types cover large part of the diagram. I said “approximate” because the classification principles used to classify plutonic and volcanic rocks are in most cases different. This rock type is found in a wide variety of colors. Common accessory minerals are zircon, apatite, sphene, magnetite, and ilmenite. Most minerals fall within these two broad groups.…. Felsic rocks are light in color and are composed of feldspars and silicates. and perthosite (alkali feldspar syen.) Additionally, they contain somewhat more gas than do the ultramafic magmas, but not nearly so much as the felsic magmas. Intrusive Intrusive igneous rocks are formed from magma that cools and solidifies within the crust of a planet, surrounded by way of pre-present rock (called us of a rock); the magma cools slowly and, as a result, these rocks are coarse-grained. The older White Mountain series essentially consists of silica-saturated felsic (syenite to alkali granite) igneous rocks. By signing up for this email, you are agreeing to news, offers, and information from Encyclopaedia Britannica. For similar determinations, glasses can also be prepared in the laboratory from crystalline rocks. 2) The felsic component, isotopically represented by the quartz syenite, was derived from the partial melting of ancient crustal material, and it has the isotopic characteristics of initial 87 Sr/ 86 Sr > 0.70796, ε Nd (t) < −10.4, and ε Hf (t) < −12.4. The most notable difference is the absence or very low quantity of quartz while it is an essential component of granite. The volcanic equivalent of syenite is trachyte. The rocks are mostly pale colored, ... Phonolite is an uncommon extrusive rock, of intermediate chemical composition between felsic and mafic, with texture ranging from aphanitic (fine-grain) to porphyritic. Intrusive rocks also can be categorized consistent with the shape and size of the intrusive body and its relation t… which is rich in sodium) is trachyte. 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 are intermediate, with an average silica content of 59 percent; gabbro and basalt are mafic, with an average silica content of 48 percent; and peridotite is Updates? Subsequently, one may also ask, is granite mafic felsic or intermediate? Dark mica biotite and amphibole hornblende are usual mafic constituents. which contains almost no plagioclase. The Astrophyllite Bay Complex in East Greenland (part of the Palaeogene North Atlantic Igneous Province) consists of an alkaline diorite plug, with detached trachyandesitic pillows, surrounded by co-magmatic syenite that was emplaced into Archaean basement. Additionally they tried on the extender to construct the ultimate resting places of the important leaders and individuals of means (the pyramids). Syenite is an igneous rock that solidified slowly in the crust in a similar manner to granite. 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. Felsic and mafic rocks, division of igneous rocks on the basis of their silica content. Wikipedia The abundant dark-coloured minerals include olivine, pyroxene, amphibole, biotite, garnet, tourmaline, iron oxides, sulfides, and metals. Omissions? Most syenitic seem to be associated with extensional tectonic regime (rifting continents). It exhibits a characteristic schiller, but larvikite contains more plagioclase than alkali feldspar and is therefore monzonite. It is believed to form from the cooling of magma that forms at very high temperatures and at great depths. The mineral grains in such rocks can generally be recognized with the bare eye. Foid syenites contain significant amount of relatively rare silicate minerals known as feldspathoids (F) which are called foids for simplicity. The term “syenite” is actually an ancient one. Intermediate rocks are composed of the minerals amphibole and feldspar and contain a combination of light and dark minerals. 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 are intermediate, with an average silica content of 59 percent; gabbro and basalt are mafic, with an average silica content of 48 percent; and peridotite is an ultramafic rock, with an average of 41 percent silica. Alkali feldspar forming the majority of most syenitic rocks is usually intergrown with sodium-rich plagioclase feldspar (usually oligoclase). 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, … There is a town named Syene (nowadays: Aswan) in Egypt. Mafic enclaves hosted by the quartz syenite provide direct evidence for the involvement of mantle-derived magmas in the generation of the quartz syenite. Gabbro is the name given to intrusive mafic rocks, whereas basalt is the name given to extrusive mafic rocks. Mafic dykes have evidence of partial melting forming leucosomes with large peritectic augite in a syenitic matrix. 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. The diagram above may leave us an impression that the true syenite is a relatively insignificant part of the whole family. Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree.... Get a Britannica Premium subscription and gain access to exclusive content. The term “syenite” in a wider sense involves similar rock types like quartz syen., alkali feldspar syenite, foid syen., foid monzosyenite, etc. ... 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. The central part of this nepheline syenite is very white felsics with black mafics in it. The diorite intrusion has yielded a 47.11 ± 0.68 Ma Rb-Sr isochron age. 2a). Alkali Syenite Mineralogy A syenite rich in sodium, this rock has strongly perthitic K-spars or anorthoclase Plagioclase is albite to sodic oligoclase Mafic minerals include iron-rich biotite, iron or sodic amphiboles including hastingsite, arfvedsonite, or riebeckite, and pyroxene is either aegirine-augite or aegirine Occurrence of igneous rocks can be either intrusive (plutonic) or extrusive (volcanic). 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. They form relatively small intrusive bodies or parts of larger intrusions. Both mafic and syenitic dykes interact with marble forming highly irregular margins, mingling features and different kinds of … 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 are intermediate, with an average silica content of 59 percent; gabbro and basalt are mafic, with an average silica content of 48 percent; and peridotite is an ultramafic rock, with an average of 41 percent silica. 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 are intermediate, with an average silica content of 59 percent; gabbro and basalt are mafic, with an … Uncommon extrusive rock, of intermediate chemical composition between felsic and mafic, with texture ranging from aphanitic to porphyritic (mixed fine- and coarse-grain). However, the rocks near that town after which this rock got its name are actually hornblende-bearing granites according to modern classification principles. In this sense it is again similar to granite which is also defined solely by its mineralogical composition although there are very different possible ways how granitic magma can evolve. (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. Syenitic rocks are mostly composed of alkali feldspar (A) with minor amounts of quartz (Q). 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. Similar to granite but has a higher percent of mafic material, intrusive, intermediate-mafic Silica content is especially useful because the density and refractive index of natural glasses have been correlated with silica percentage; this makes identification possible in the absence of chemical data. as coarse-grained plutonic rocks are porphyraceous. Mafic rocks are darker and are composed of magnesium and iron. The quartz syenite is composed of 70–75% subhedral perthite, 10–15% quartz and 10% hornblende. Actually, this is not true. Of the oxides, silica (SiO2) is usually the most abundant. The classification principles are shown on the diagram below. Hence, rhyolite and basalt as fine-grained volcanic rocks are porphyritic and granite, syenite, etc. Although there are complete gradations between the averages, rocks tend to cluster about the averages. Note that Q and F are mutually exclusive. Mafic rocks are only significant in the Pliny Range. Start studying Igneous Rock Quiz 2. 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. The approximate extrusive (volcanic) equivalent of syenite (more precisely alkali syen. Alkali syenites may contain somewhat unusual minerals like aegirine, arfvedsonite, etc. Nepheline syenite is a holocrystalline plutonic rock that consists largely of nepheline and alkali feldspar. The quartz syenite is grey, medium to coarse grain and massive, which was intruded by several felsic dikes observed in the field (Fig. Felsic rocks are commonly oversaturated and contain free quartz (SiO2), intermediate rocks contain little or no quartz or feldspathoids (undersaturated minerals), and mafic rocks may contain abundant feldspathoids. Felsic, intermediate and mafic igneous rocks differ in their mineral composition. 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%).Some syenites contain larger proportions of mafic components and smaller amounts of felsic material than most granites; those are classed as being of intermediate composition. 27 26 Mafic intrusive rocksi, mafic dikes and mafic sills 26a Molson mafic dike swarm (circa 1889 to 1871 Ma) and mafic … Nepheline syenite. Be on the lookout for your Britannica newsletter to get trusted stories delivered right to your inbox. Phonolite is an approximate equivalent of foid syenite. The true syenites are rocks that fit into the area annotated in red. In geology, felsic is an adjective describing igneous rocks that are relatively rich in elements that form feldspar and quartz. 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Very low quantity of quartz ( Q ) F ) which are called foids simplicity!