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anorthite

 
Dictionary: an·or·thite   (ăn-ôr'thīt) pronunciation
n.
A rare plagioclase feldspar with high calcium oxide content occurring in igneous rocks.

[From Greek an-, not; see a-1 + orthos, straight (from its oblique crystals).]

anorthitic an'or·thit'ic (-thĭt'ĭk) adj.

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Feldspar mineral, calcium aluminosilicate (CaAl2Si2O8), that occurs as white or grayish, brittle, glassy crystals. Primarily a rock-forming mineral, it is used in the manufacture of glass and ceramics. Anorthite occurs in basic igneous rocks (see acid and basic rocks).

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Sci-Tech Encyclopedia: Anorthite
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The calcium-rich plagioclase feldspar with composition Ab0An100 to Ab10An90 (Ab = NaAlSi2O8; An = CaAl2Si2O8), occurring in olivine-rich igneous rocks and rare volcanic ejecta (for example, at Mount Vesuvius, Italy, and Miyakejima, Japan). Hardness is 6 on Mohs scale, specific gravity 2.76, melting point 1550°C (2822°F). The crystal structure of Ab0An100 consists of an infinite three-dimensional array of corner-sharing [AlO4] and [SiO4] tetrahedra, alternately linked together in a framework of [Al2Si2O8]2− composition in which charge-balancing calcium (Ca2+) cations occupy four distinct, irregular cavities. Natural anorthite has no commercial uses, but the synthetic material [CaO · Al2O3 · 2SiO2 (known as CAS2)] is important in the ceramic industry and in certain composite materials with high-temperature applications. See also Feldspar.


WordNet: anorthite
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Note: click on a word meaning below to see its connections and related words.

The noun has one meaning:

Meaning #1: rare plagioclastic feldspar occurring in many igneous rocks


Wikipedia: Anorthite
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Anorthite

Anorthite from Japan
General
Category Feldspar mineral
Chemical formula CaAl2Si2O8
Identification
Color White, grayish, reddish
Crystal habit Anhedral to subhedral granular
Crystal system Triclinic
Twinning Common
Cleavage Perfect [001] good [010] poor [110]
Fracture Uneven to concoidal
Tenacity Brittle
Mohs scale hardness 6
Luster Vitreous
Diaphaneity Transparent to translucent
Specific gravity 2.72 - 2.75
Optical properties Biaxial (-), 2V 78° to 83°
Refractive index nα = 1.573 - 1.577 nβ = 1.580 - 1.585 nγ = 1.585 - 1.590
Birefringence δ = 0.012 - 0.013
References [1][2][3]

Anorthite is the calcium endmember of plagioclase feldspar. Plagioclase is an abundant mineral in the Earth's crust. The formula of pure anorthite is CaAl2Si2O8.

Contents

Mineralogy

Anorthite is the calcium-rich endmember of the plagioclase solid solution series, the other endmember being albite, NaAlSi3O8. Anorthite also refers to plagioclase compositions with more than 90 molecular percent of the anorthite endmember.

Occurrence

Anorthite is a rare compositional variety of plagioclase. It occurs in mafic igneous rock. It also occurs in granulite facies metamorphic rocks, in metamorphosed carbonate rocks and corundum deposits.[1] Its type localities are Monte Somma and Valle di Fassa, Italy. It was first described in 1823.[3]

It also makes up much of the lunar highlands; the Genesis Rock is made of anorthosite, which is composed largely of anorthite. 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.

See also

References


 
 
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Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.  Read more
Britannica Concise Encyclopedia. Britannica Concise Encyclopedia. © 2006 Encyclopædia Britannica, Inc. All rights reserved.  Read more
Sci-Tech Encyclopedia. McGraw-Hill Encyclopedia of Science and Technology. Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved.  Read more
WordNet. WordNet 1.7.1 Copyright © 2001 by Princeton University. All rights reserved.  Read more
Wikipedia. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article "Anorthite" Read more

 

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