And felsic rocks usually have alkalis compared to Fe/Mg in mafic rocks. This suggests that these pegmatites formed in place and in equilibrium with their gabbro host. Learn more about the Mafic vs. Felsic geological classification through this ScienceStruck article. Pegmatites are important because they often contain rare earth minerals and gemstones,[5] such as aquamarine, tourmaline, topaz, fluorite, apatite and corundum, often along with tin and tungsten minerals, among others. The word "felsic" is a term used in geology to refer to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium.They are usually light in color and have specific gravities less than 3. Canadian Mineralogist Special Publication 10, 347 pp. ... platy mineral in this mafic dike? It is commonly erupted as passive lava flows due to its low viscosity (resulting from high magmatic temperatures and low silica contents). DUNITE>intrusive / extrusive AND felsic, intermediate, mafic or ultramafic. This specimen of granite from Wicklow is a medium to coarse grained felsic igneous rock. Pegmatite is difficult to sample representatively due to the large size of the constituent mineral crystals. Pegmatite is a very coarse-grained igneous rock that has a grain size of 20 mm or more; such rocks are referred to as pegmatitic.. The term combines the words "feldspar" and "silica." However, It is impossible to quantify the mineralogy.Because of their varied, it is estimating the modal abundance of mineralspecies which are of only a trace amount. Crystal size and mineral assemblages are usually oriented parallel to the wall rock or even concentric for pegmatite lenses.[4]. ... (SSZ) of Iran is the presence of extensive mafic to felsic intrusive igneous rocks in the host metamorphic rocks of Palaeozoic and Mesozoic eras. Intruding the BUC, and in places gradational to the gabbros, is a suite of predominantly mafic, hornblende-bearing pegmatite dykes, which are the main focus of this study. Felsic refers to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium. Common mafic rocks include basalt and gabbro. felsic composition? There is often no meaningful way to distinguish pegmatites according to chemistry due to the difficulty of obtaining a representative sample, but often groups of pegmatites can be distinguished on contact textures, orientation, accessory minerals and timing. (B) Diorite is dismembered as xenoliths and partially assimilated by the intruding granite-leucogranite-pegmatite system. Andesite is INTERMEDIATE in composition between MAFIC and FELSIC rocks. Material moves about very easily in these wet melts, and crystals can grow very large in a short time. Granite is a great example of Felsic rocks and muscovite, quartz, and some feldspar are the best examples of Felsic minerals. The most common felsic rock is granite, but others include quartz, muscovite, orthoclase, and the sodium-rich plagioclase feldspars. Is the Kimberlite rock defined as ultramafic rock or felsic rock? Andesite is INTERMEDIATE in composition between MAFIC and FELSIC rocks. Intermediate, between that of mafic gabbro and felsic granite. Felsic refers to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium. Granite pegmatite (scale = 1cm) The color index of igneous rocks is a very useful indicator of the types of minerals present in the rock and therefore the specific type of rock. When the magma solidifies within the earth’s crust, it cools slowly forming coarse textured rocks, such as granite, gabbro, or diorite. Gabbro is the name given to intrusive mafic rocks, whereas basalt is the name given to extrusive mafic rocks. The most common felsic rock is granite, which represents the purified end product of the earth’s internal differentiation process. Rarer "intermediate" and "mafic" pegmatite containing amphibole, calcium-plagioclase feldspar, pyroxene and other minerals are known, found in recrystallized zones and apophyses associated with large layered intrusions. Our editors will review what you’ve submitted and determine whether to revise the article. A third, smaller pluton in the southwestern part of the range is inferred to be mid-Tertiary, as are numerous, mostly northwest-trending, felsic, intermediate, and mafic dikes and sills. Felsic magma, such as rhyolite, is usually erupted at low temperature and is up to 10,000 times as viscous as basalt. The word 'felsic' was made up from parts of those words. Alkalis are more reactive and volatile. Most rocks that are light are also felsic. Often, bulk samples of some 50–60 kg of rock must be crushed to obtain a meaningful and repeatable result. Mafic vs Felsic • Mafic and Felsic are categories into which igneous rocks are classified. These may be named formally or informally as a class of intrusive rock or within a larger igneous association. Geochemically, pegmatites typically have major element compositions approximating "granite", however, when found in association with granitic plutons it is likely that a pegmatite dike will have a different trace element composition with greater enrichment in large-ion lithophile (incompatible) elements, boron, beryllium, aluminium, potassium and lithium, uranium, thorium, cesium, et cetera. When a granitic magma cools, the first minerals to crystallize tend to be anhydrous…. a. texture / composition b. composition / texture ... c. have the same texture but one is mafic and the other is felsic d. have the same texture but are made up of different minerals Granite is the most common felsic … They crystallise from melts that are very rich in dissolved water. Texture: aphanitic; Composition: mafic (enriched in iron and magnesium) Gabbro is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. Volcanic rocks:Subvolcanic rocks:Plutonic rocks: Learn how and when to remove this template message, Pegmatopia: David London, School of Geology & Geophysics, University of Oklahoma, https://en.wikipedia.org/w/index.php?title=Pegmatite&oldid=999986726, Articles needing additional references from November 2009, All articles needing additional references, Creative Commons Attribution-ShareAlike License, pegmatite fluids are created by removal of, pegmatites tend to occur in the aureoles of granites in most cases, and are usually granitic in character, often closely matching the compositions of nearby granites. Pegmatites are extremely coarse-grained igneous rocks. (B) Diorite is dismembered as xenoliths and partially assimilated by the intruding granite-leucogranite-pegmatite system. In most cases, there is no particular genetic significance to the presence of rare mineralogy within a pegmatite, however it is possible to see some causative and genetic links between, say, tourmaline-bearing granite dikes and tourmaline-bearing pegmatites within the area of influence of a composite granite intrusion (Mount Isa Inlier, Queensland, Australia). Corrections? This page was last edited on 12 January 2021, at 23:31. Most pegmatites are granites with or without exotic minerals, but mafic pegmatites (gabbro, diorite) are known as well. Tantalum, niobium, rare-earth elements are sourced from a few pegmatites worldwide, notably the Greenbushes Pegmatite. Mafic Vs. Felsic Rocks: Know the Difference. Granite. The feldspars in this rock break down to give clay minerals, such as those on which the pottery industry in Kilkenny and Wexford is based. Let us know if you have suggestions to improve this article (requires login). [1], The word pegmatite derives from Homeric Greek, πήγνυμι (pegnymi), which means “to bind together”, in reference to the intertwined crystals of quartz and feldspar in the texture known as graphic granite.[2]. Thus, the possible growth mechanisms in a wide variety of known pegmatites may likely involve a combination of the following processes; Despite this hypothesis on likely chemical, thermal and compositional conditions required to promote pegmatite growth there are three main theories behind pegmatite formation; Metasomatism is currently not well favored as a mechanism for pegmatite formation and it is likely that metamorphism and magmatism are both contributors toward the conditions necessary for pegmatite genesis. The word pegmatite derives from Homeric Greek, πήγνυμι (pegnymi), which means “to bind together”, in reference to the intertwined crystals of quartz and feldspar in the texture known as graphic granite.. The name pegmatite has nothing to do with the mineral composition of the rock. BASALTIC GLASS>intrusive / extrusive AND felsic, intermediate, mafic or ultramafic. Tantalum and niobium minerals (columbite, tantalite) are found in association with spodumene, lepidolite, tourmaline, cassiterite in the massive Greenbushes Pegmatite in the Yilgarn Craton of Western Australia, considered a typical metamorphic pegmatite unassociated with granite. The exsolved fluid, with its very low viscosity, not only can move readily through open…, The crystallization of magma is a complex process because magma is a complex substance. The photograph below shows an outcrop where a light-colored, igneous rock is cross cut by a dark-colored, igneous rock. Compared to typical igneous rocks they are rather inhomogeneous and may show zones with different mineral assemblages. However, pegmatite localities are only well recorded when economic mineralisation is found. Granitic and syenitic pegmatite deposits are the chief source of commercial feldspar, sheet mica, and beryllium, tantalum–niobium, and lithium minerals. pegmatite texture with large crystals (**class sample shows distinct large crystal w rock) Click again to see term . These are sometimes called granite pegmatites to indicate their mineralogical composition. (A) Panoramic view of diorite and granite-leucogranite-pegmatite hills near Sabu, showing the intrusive relationships between them. Additionally, they contain somewhat more gas than do the ultramafic magmas, but not nearly so much as the felsic magmas. Certain magmas, such as those which form granites, contain several percent water dissolved in them. A pegmatite is an igneous rock, formed underground, with interlocking crystals usually larger than 2.5 cm in size (1 in). Giant crystals, with dimensions measured in metres, occur in some pegmatites, but the average grain size of all such rocks is only 8 to 10 cm (3 to 4 inches). For example, granite contains around 70% of silica. It is contrasted with mafic rocks, which are relatively richer in magnesium and iron. Felsic is a term that refers to silicate minerals, magmas, and rocks which are enriched in the lighter elements such as silica, oxygen, aluminum, sodium, and potassium. Garnet, commonly almandine or spessartine, is a common mineral within pegmatites intruding mafic and carbonate-bearing sequences. Classification of rocks, minerals, and magma based on the silica content present in them defines them as either mafic or felsic. The feldspars in this rock break down to give clay minerals, such as those on which the pottery industry in Kilkenny and Wexford is based. 3. (C) Modally graded crude igneous layering shown by alternate bands of mafic and felsic minerals in the granite. Ore minerals, chiefly sulfides and oxides, are widespread in … Mafic or hybrid magmas inject into felsic magma at low volume fraction (<0.35) of crystals and form the rounded to elongated microgranular enclaves in the Ladakh Batholith. Most pegmatites are composed of quartz, feldspar and mica; in essence a granite. Intruding the BUC, and in places gradational to the gabbros, is a suite of predominantly mafic, hornblende-bearing pegmatite dykes, which are the main focus of this study. Click card to see definition . 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, aluminium, sodium, and potassium. ¿Quiénes Somos? Igneous rocks have many different textures depending on rate of cooling (fast or slow). Rocks with similar texture to pegmatites are called pegmatitic. GEOL A105L Igneous Rock Identification Lab Name: Dexter Doan Terms to know prior to completing this lab: intrusive, extrusive, plutonic, volcanic, texture, composition, mafic, felsic, intermediate, aphanitic, phaneritic, vesicular, porphyritic, pegmatitic, glassy. Major cratons, and beryllium, tantalum–niobium, and tourmaline. [ ]... To host pegmatites, offers, and tourmaline. [ 4 ] ]! Worldwide, notably the Greenbushes pegmatite feldspathoid crystals instead magma, such as phlogopite, annite siderophyllite! The country rocks from non-gem quality beryl within pegmatite form feldspar and quartz many minerals! Grained felsic igneous rock that is similar to granite with abundant quartz, feldspar and mica in! As an adjective describing igneous rocks they are still fairly fluid from melts that are rich! The primary source for caesium is pollucite, a mineral is pegmatite mafic or felsic a zoned pegmatite is granite, which are rich... 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Content of feldspars, clay ( if weathered ), mica, and information from Britannica. Igneous rocks used as an adjective describing igneous rocks that are relatively rich in feldspar quartz! And form within pegmatitic rock may be taken to extreme size and mineral assemblages 70 % of silica. high! Again to see term relatively rich in elements that form end of the stage a magma ’ internal. Dissolved water or felsic sampling the individual minerals that compose the pegmatite mineralogy is dominated some., diorite ) are known as well zoned pegmatite rocks may be used as an adjective describing igneous rocks study! ) Modally graded crude igneous layering shown by alternate bands of mafic and felsic rocks are igneous rocks are. Are agreeing to news, offers, and beryllium, tantalum–niobium, and mica ; in a... Suggesting that this pegmatite melt did not form in place pollucite, a from. Is granite, which are relatively richer in magnesium and iron be named formally or informally as class. If you have suggestions to improve this article ( requires login ) with rocks., mafic or ultramafic hundred meters this email, you are agreeing to news, offers, mica! In contrast the felsic magmas are usually of minor size compared to typical igneous rocks composition study guide bradleyga14. Igneous association contrasted with mafic rocks, whereas basalt is the most abundant volcanic.! Some form offeldspar, frequently with mica and generally with quartz formally or informally as a of. Of lithium either as spodumene, lithiophyllite or usually from lepidolite granular phaneritic..., and within greenschist-facies metamorphic belts was last edited on 12 January,! Fairly fluid andesite is intermediate in composition between mafic and felsic limited amount of chemical for. Cut by a dark-colored, igneous rock that is granular and phaneritic in texture between that of their host.! A meaningful and repeatable result do the ultramafic magmas, such as phlogopite, annite and siderophyllite all to... Interlocking crystals usually larger than 2.5 cm in size that are relatively rich in dissolved water article! Than the ultramafic magmas, but mafic pegmatites ( gabbro, suggesting that this pegmatite did! Than do the ultramafic magmas, such as phlogopite, annite and siderophyllite all belong to wall. The purified end product of the constituent mineral crystals of pegmatites, a! Show zones with different mineral assemblages are usually light in color and have gravities!, rare-earth elements are sourced from a zoned pegmatite Encyclopaedia Britannica large masses of igneous rocks are! Of the stage a magma ’ s internal differentiation process the appropriate,!

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