[online] Available at: https://geologyscience.com/rocks/igneous-rocks/intrusive-igneous-rocks/gabbro/ [3rd December 2020 ], Economically Important Metal Concentrations in Earth’s Crust, Porphyry Deposits: General characteristics and modeling, Igneous Rocks: A Classification and Glossary of Terms: Recommendations of the International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks, https://geologyscience.com/rocks/igneous-rocks/intrusive-igneous-rocks/gabbro/, Ronald Louis Bonewitz, (2012) NATURE GUIDE AND MINERALS, Smithsonian NATURE GUIDE, LONDON, NEW YORK, MELBOURNE, MUNICH, AND DELHI. A gabbroid composed of 10-90% Ca-dominant plagioclase and >5% clinopyroxene. Classification of Igneous Rocks by Russell B. Travis Web pages adapted from Quarterly of the Colorado School of Mines, vol. Some of the special terms used are:Gabbro (sensu stricto) = plagioclase and clinopyroxeneNorite = plagioclase and orthopyroxeneTroctolite = plagioclase and olivineGabbronorite = plagioclase with almost equal amounts of clinopyroxene and orthopyroxeneOrthopyroxene gabbro = plagioclase and clinopyroxene with minor amounts of orthopyroxene. The former was altered to scapolite and the latter to hornblende. The hot magma inside the earth is the basic source of all minerals. ; The earth is made of igneous rock – at least at the surface where our planet is exposed to the coldness of space. Diorite, gabbro, anorthosite — the three root names in this field are separated according to the colour index and the average composition of their plagioclase – anortho… (The pyroxene-dominated gabbroids are either true gabbro or norite, depending on whether the pyroxene is … It is often mentioned that the term “gabbro” was brought into geological terminology by a German geologist Leopold von Buch. Classification of Norite Hide There is a gabbro Intermediate or low silica content and rarely contains quartz. Originally the rock was composed of plagioclase and pyroxene. The procedure follows two complementary steps at two different levels. Olivine gabbro also contains olivine in addition to plagioclase and cpx. Olivine can be present or feldspathoids just like in basalt. Gabbro occurs when the liquid rock is cooled very slowly over a long period of time in the underground. Gabbro can be polished to a bright black glow. If quartz makes up more than 20%, then the rock is one of granitoids1. Classification of common igneous rocksComposition Phaneritic Aphanitic Color index (% dark minerals)Felsic Granite Rhyolite 10 Syenite Trachyte 15 Monzonite Latite 20Intermediate Granodiorite Dacite 20 Diorite Andesite 25Mafic Gabbro Basalt 50Ultramafic Peridotite 95 The term gabbro was used originally by Italian geologist Tozzetti in 1768 and brought into geological terminology by a German geologist Leopold von Buch. Picture taken in a gabbro quarry in southeastern Norway. Troctolite contains mostly olivine and plagioclase, pyroxene again forms no more than 10% of the composition. Cumulate gabbros are more properly termed pyroxene-plagioclase orthocumulate. Flakstadøya, the Lofoten Archipelago, Norway. It is a small amount of olivine and amphibole. The classification scheme for gabbroic rocks without taking into account olivine and feldspathoids. Tappeluft, Norway. This sample of gabbro comes from La Plama. The time required for the liquid rock to cool will determine the texture.On the other hand, the basalt is an extrusive magmatic rock. If there is more sodium in the plagioclase, then the rock type is called diorite. 1) Size Classification. Le Maitre, R. W. (2005). Norite may be very similar to gabbro but contains orthopyroxene, not clinopyroxene. In the IUGS classification gabbro contains 0-5% Q, P/(A + P) >90, pl/(pl + px + ol) is 10 - 90, and the plagioclase composition > An 50. Texture Alkali Feldspar Sodium Plagioclase Calcium Plagioclase Phaneritic Granite Diorite Gabbro Aphanitic Rhyolite Andesite Basalt Geoscientists at the University of British Columbia has prepared a nice figure which summarizes information about the Classification of Igneous Rocks . Basalt. Gabbro: A coarse-grained plutonic rock composed essentially of calcic plagioclase, pyroxene and iron oxides. “Olivine” should be added to the rock name if it contains more than 10% of it. The studied soils were ~ 2 m thick, made of four horizons which consisted of coarse saprolite, fine saprolite, loose loamy clayey horizon and humiferous horizon. It means that it formed as magma cooled slowly in the crust. Pyroxenite and other ultramafic rocks are darker- and diorite is lighter-colored. If more than 95% of the pyroxene is Opx, then we have norite. Chemical composition of an average gabbro? Width of sample 5 cm. Gabbro is actually intrusive basalt equivalent, but unlike basalt gabbro it has a variable variable mineral content. BC. These colors are not real, they are caused by the interference between lightwaves. X or R 1 = 4 Si − 11(Na+K) − 2(Fe+Ti) and Y or R 2 = 6 Ca+ 2Mg+ Al. Luster of Gabbro is not available and its fracture is conchoidal. 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