Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Plagioclase is the name of a group of feldspar minerals that form a solid solution series ranging from pure albite, Na(AlSi3O8), to pure anorthite, Ca(Al2Si2O8). The chemical formula of pure anorthite is Ca Al 2 Si 2 O 8. Mineralogy. Primarily a rock-forming mineral, it is used in the manufacture of glass and ceramics. The chemical formula of pure anorthite is CaAl2Si2O8. The feldspar minerals are mixtures of sodium, potassium, and calcium aluminosilicates; they belong to a ternary system in which any mineral may be classed by its percentage of each of three pure compounds, called end-members: sodium aluminosilicate, potassium aluminosilicate, and calcium aluminosilicate. Corrections? Anorthite is the rarest member of the Plagioclase Feldspars of the Feldspar Group of minerals that includes Albite, Amazonite, Andesine, Anorthite, Bytownite, Hyalophane, Labradorite, Moonstone, Oligoclase, Orthoclase, Sanidine and Sunstone. A series between Albite and Anorthite Feldspar Group. It occurs in mafic igneous rock. Anorthite is rare on the Earth but abundant on the Moon. The minerals of the plagioclase series are listed in the table below along with their relative abundance of albite (Ab) and anorthite (An). It was first described in 1823. Omissions? Updates? The chemical formula of pure anorthite is Ca Al 2 Si 2 O 8. Anorthite is rare on the Earth but abundant on the Moon. The formula of pure anorthite is CaAl 2 Si 2 O 8.It is not Radioactive. [6], Anorthite is the calcium-rich endmember of the plagioclase solid solution series, the other endmember being albite, NaAlSi3O8. Anorthite is a lime feldspar, triclinic, has a hardness f 6 to 6.5 mhos, SG of 2.7 - 2.8, is white, usually, can be colorless or grayish, bluish, yellowish or reddish. This article was most recently revised and updated by, https://www.britannica.com/science/anorthite, The Mineral and Gemstone Kingdom - Anorthite, Amethyst Galleries - The Mineral Anorthite. Anorthite is the calcium endmember of the plagioclase feldspar mineral series. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more properly known as the plagioclase feldspar series. Anorthite. Similarly, for an olivine ... KALSi 3 O 8, and Anorthite (An) - CaAl2Si 2 O 8. Anorthite and the sodium-bearing end-member of the system, albite (NaAlSi3O8), form a solid-solution series in which the two intermingle; thus, in nature there is a continuous chemical variation between the two compounds. The Anorthite Na0:1¡0:0Ca0:9¡1:0Al1:9¡2:0Si2:1¡2:0O8 °c 2001 Mineral Data Publishing, version 1.2 Crystal Data: Triclinic. The other end member, Anorthite, contains calcium and no sodium.The intermediary members are Oligoclase, Andesine, Labradorite, and Bytownite.Oligoclase and Andesine are considered by some to be a variety of Albite rather then a separate mineral. Primarily a rock-forming mineral, it is used in the manufacture of glass and ceramics. Anorthite is rare on the Earth[5] but abundant on the Moon. The names of the minerals in the series are arbitrarily given based upon their relative abundance of albite and anorthite. ... Anorthite formula. Multiply all of the normative ‘mineral’ values by their respective formula weights. Anorthite is found in mafic igneous rocks. Anorthite is found in mafic igneous rocks. By signing up for this email, you are agreeing to news, offers, and information from Encyclopaedia Britannica. Anorthite is rare on the Earth [5] but abundant on the Moon. Albite belongs to the Plagioclase Feldspar group, an isomorphous solid solution series.Albite is one end member, containing sodium and no calcium. Anorthite, a feldspar mineral, calcium aluminosilicate (CaAl2Si2O8), that occurs as white or grayish, brittle, glassy crystals. At 1 atmosphere, anorthite melts at 1553 °C.[1]. The composition of plagioclase feldspar is typicallyindicated by the general anorthite (% An) or albite (% Ab) fraction and iseasily determined by measuring the refractive index or peel angle within thecrushed particles by measuring the refraction angle under a thin section. Anorthite is an end member and one of the rarer members of the plagioclase series. Anorthite could be the member that is rarest of Plagioclase Feldspars for the Feldspar number of minerals that includes Albite, Amazonite, Andesine, Anorthite, Bytownite, Hyalophane, Labradorite, Moonstone, Oligoclase, Orthoclase, Sanidine and Sunstone. Premium Membership is now 50% off! Tremolite formula (amphibole) Ca2Mg5Si8O22(OH)2. The plagioclase series comprises minerals that range in chemical composition from pure NaAlSi3 O8, Albite to pure CaAl2 Si2 O8 , anorthite.Anorthite by definition must contain no more than 10% sodium and no less than 90% calcium in the sodium/calcium position in the crystal structure. 65, 272-284, CS1 maint: multiple names: authors list (, http://www.minsocam.org/ammin/AM65/AM65_272.pdf, https://en.wikipedia.org/w/index.php?title=Anorthite&oldid=900201759, Creative Commons Attribution-ShareAlike License, This page was last edited on 4 June 2019, at 03:00. The Plagioclase Feldspars form a series between Albite and Anorthite. Feldspar Na Endmember NaAlSi3O8. Anorthite is the calcium endmember of plagioclase feldspar. Anorthite occurs in basic igneous rocks, as at Trentino, Italy; Södermanland, Swed. Plagioclase is an abundant mineral in the Earth’s crust. Anorthite was discovered in samples from comet Wild 2, and the mineral is an important constituent of Ca-Al-rich inclusions in rare varieties of chondritic meteorites. Plagioclase: Add albite to anorthite to make plagioclase. Anorthite Anorthite is the calcium endmember of plagioclase feldspar. Thedeflection angle is an optical characteristic and varies according to thealbite fraction (Ab). The chemical formula of pure anorthite is CaAl2Si2O8. The chemical formula for such a composition would be written as MgFeSiO 4. May contain some sodium replacing the calcium, but that amount must be less than 10 percent to be strictly Anorthite. Anorthite is the calcium endmember of the plagioclase feldspar mineral series. Any member of this series is called a plagioclase. Minerals in this series are a homogenous mixture of albite and anorthite. Anorthite is found in mafic igneous rocks. Anorthite is rare on the Earth but abundant on the Moon. Anorthite is found in mafic igneous rocks. Plagioclase is an abundant mineral in the Earth's crust. Anorthite is the calcium-rich endmember of the plagioclase solid solution series, the other endmember being albite, NaAlSi3O8. CaAl2Si2O8. It also makes up much of the lunar highlands; the Genesis Rock is made of anorthosite, which is composed largely of anorthite. [4] It is more rare in surficial rocks than it normally would be due to its high weathering potential in the Goldich dissolution series. In thin section, plagioclase feldspar grains often look like they’re sprinkled with dirt (PPL) or tiny confetti (XPL). Anorthite is a rare compositional variety of plagioclase. The feldspar group ) in 1826 1-An ' ) * 262.2230 ).. Gray feldspar mineral, CaAl2Si2O8, calcic plagioclase to revise the article Nadu India. Weight of plagioclase = ( an ' value from # 24 signing up for this email, are... Of glass and ceramics calcium is a series of tectosilicate ( framework silicate ) minerals within feldspar. 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