Anorthite
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Anorthite is the
calcium Calcium is a chemical element with the Symbol (chemistry), symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties a ...

calcium
endmember An endmember (also end-member or end member) in mineralogy Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical mineralogy, optical) properties of minerals and ...
of the
plagioclase . (unknown scale) Plagioclase is a series of Silicate minerals#Tectosilicates, tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagiocla ...
feldspar Feldspars () are a group of rock-forming tectosilicate minerals that make up about 41% of the Earth's continental crust by weight. Feldspars crystallize from magma as both Intrusive rock, intrusive and extrusive igneous rocks and are also pres ...
mineral series. The chemical formula of pure anorthite is
Ca
Ca
Al2
Si
Si
2
O
O
8. Anorthite is found in
mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole Amphibole () is a group of Silic ...
igneous rock Igneous rock (derived from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the p ...
s. Anorthite is rare on the Earth but abundant on the Moon.


Mineralogy

Anorthite is the
calcium Calcium is a chemical element with the Symbol (chemistry), symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties a ...

calcium
-rich
endmember An endmember (also end-member or end member) in mineralogy Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical mineralogy, optical) properties of minerals and ...
of the plagioclase
solid solution A solid solution describes a family of materials which have a range of compositions (e.g. AxB1−x) and a single crystal structure. Many examples can be found in metallurgy, geology, and solid-state chemistry. The word "solution" is used to desc ...

solid solution
series, the other endmember being
albite Albite is a plagioclase feldspar Feldspars () are a group of rock-forming tectosilicate minerals that make up about 41% of the Earth's continental crust by weight. Feldspars crystallize from magma as both Intrusive rock, intrusive and extru ...
,
Na
Na
AlSi3O8. Anorthite also refers to plagioclase compositions with more than 90
molecular A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral group of two or more atom An atom is the smallest unit of ordinary matter In ...
percent of the anorthite endmember. At 1 atmosphere, anorthite melts at 1553°C.J.R. Goldsmith (1980): The melting and breakdown reactions of anorthite at high pressures and temperatures. Am. Mineralogist. 65, 272-284, http://www.minsocam.org/ammin/AM65/AM65_272.pdf


Occurrence

Anorthite is a rare compositional variety of plagioclase. It occurs in
mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole Amphibole () is a group of Silic ...
igneous rock Igneous rock (derived from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the p ...
. It also occurs in
metamorphic rock
metamorphic rock
s of
granulite Granulites are a class of high-grade metamorphic rocks of the granulite facies that have experienced high-temperature and moderate-pressure metamorphism. They are medium to coarse–grained and mainly composed of feldspars sometimes associate ...

granulite
facies carbonate facies (Holocene) on Long Island, Bahamas Long Island is an island in the Bahamas that is split by the Tropic of Cancer. It is one of the Districts of the Bahamas and is known as the most scenic island in the Bahamas. Its capital is Clar ...

facies
, in metamorphosed
carbonate rock 250px, Carbonate ooids on the surface of a limestone; Carmel Formation (Middle Jurassic) of southern Utah, USA. Largest is 1.0 mm in diameter. Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two major ...
s, and
corundum Corundum is a crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all direction ...

corundum
deposits. Its type localities are
Monte Somma Mount Somma ( it, Monte Somma) is a mountain located in the Province of Naples, in the Campania region of southern Italy. Mount Somma is an integral part of the Vesuvius, Somma–Vesuvius volcanic complex. It is high. Geography Mount Somma is ...

Monte Somma
and
Valle di Fassa * 'Valley' is a name given to brave prince in certain kindoms in uganda . Like *Valley muwaga* born in 1950, was a husband to Nabirye Lovisa and atrader bringing goods from mombasa to uganda eastern region jinja district. He died in 1979 leavin ...
,
Italy Italy ( it, Italia ), officially the Italian Republic ( it, Repubblica Italiana, links=no ), is a country consisting of a Northern Italy, continental part, delimited by the Alps, a Italian Peninsula, peninsula and List of islands of Italy, se ...

Italy
. It was first described in 1823. It is more rare in surficial rocks than it normally would be due to its high weathering potential in the
Goldich dissolution series The Goldich dissolution series is a way of predicting the relative stability or weathering Weathering is the breaking down of rocks, soil Soil (often stylized as SOiL) is an American rock band that was formed in Chicago ...
. It also makes up much of the
lunar Lunar most commonly means "of or relating to the Moon". Lunar may also refer to: Arts and entertainment * Lunar (series), ''Lunar'' (series), a series of video games * Lunar (song), "Lunar" (song), by David Guetta * "Lunar", a song by Priestess fr ...

lunar
highlands; the
Genesis Rock The Genesis Rock on the lunar surface prior to sampling (left of the gnomon, which was used for scale in the photos) The Genesis Rock is a sample of Moon rock Moon rock or lunar rock refers to rock that is found on the Moon, Earth's Moon. Th ...
is made of
anorthosite Anorthosite is a phaneritic, intrusive igneous rock characterized by its composition: mostly plagioclase feldspar (90–100%), with a minimal mafic component (0–10%). Pyroxene The pyroxenes (commonly abbreviated to ''Px'') are a group o ...
, which is composed largely of anorthite. Anorthite was discovered in samples from
comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a Comet tail, tail. These ...
, and the mineral is an important constituent of Ca-Al-rich inclusions in rare varieties of chondritic meteorites.


See also

*
List of minerals This is a list of minerals for which there are articles on Wikipedia. Mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific ...


References

{{Reflist Tectosilicates Calcium minerals Feldspar Triclinic minerals Gemstones Minerals in space group 2