Anorthite is the

calcium Calcium is a chemical element with the 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 are most similar ...

endmember of the plagioclase feldspar mineral series. The chemical formula of pure anorthite is Ca Al₂ Si₂O₈. 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, and biotite. Common mafic rocks in ...

igneous rock Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma o ...

s. Anorthite is rare on the Earth but abundant on the Moon.

Mineralogy

Anorthite is the calcium-rich endmember of the plagioclase solid solution series, the other endmember being

albite Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. It represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula . It is a tectosilicate ...

(NaAlSi₃O₈). Anorthite also refers to plagioclase compositions with more than 90 molecular percent of the anorthite endmember. At standard pressure, anorthite melts at .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

. It also occurs in

metamorphic rock Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, caus ...

s of granulite

facies In geology, a facies ( , ; same pronunciation and spelling in the plural) is a body of rock with specified characteristics, which can be any observable attribute of rocks (such as their overall appearance, composition, or condition of formatio ...

, in metamorphosed carbonate rocks, and

corundum Corundum is a crystalline form of aluminium oxide () typically containing traces of iron, titanium, vanadium and chromium. It is a rock-forming mineral. It is a naturally transparent material, but can have different colors depending on the pr ...

deposits. Its type localities are Monte Somma and

Valle di Fassa Valle may refer to: * Valle (surname) Geography *"Valle", the cultural and climatic zone of the dry subtropical Interandean Valles of the Andes of Peru, Bolivia, and northwest Argentina *University of Valle, a public university in Cali, Colombia ...

Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical ...

. 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. 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), a series of video games * "Lunar" (song), by David Guetta * "Lunar", a song by Priestess from the 2009 album ''Prior t ...

highlands; the Genesis Rock, collected during the 1971

Apollo 15 Apollo 15 (July 26August 7, 1971) was the ninth crewed mission in the United States' Apollo program and the fourth to land on the Moon. It was the first J mission, with a longer stay on the Moon and a greater focus on science than ear ...

mission, is made of anorthosite, a rock 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 tail. These phenomena ...

Wild 2 Comet 81P/Wild, also known as Wild 2 (pronounced "vilt two") ( ), is a comet named after Swiss astronomer Paul Wild, who discovered it on January 6, 1978, using a 40-cm Schmidt telescope at Zimmerwald, Switzerland. For most of its 4.5 billion- ...

, and the mineral is an important constituent of Ca-Al-rich inclusions in rare varieties of chondritic meteorites.

References

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

Mineralogy

Occurrence

See also

References