albite
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al·bite
(ăl'bīt) 
n.
A widely distributed white feldspar, NaAlSi3O8, that is one of the common rock-forming plagioclase group.
n.
A widely distributed white feldspar, NaAlSi3O8, that is one of the common rock-forming plagioclase group.
[Latin albus, white + -ITE1.]
albitic al·bit'ic (-bĭt'ĭk) or al·bit'i·cal (-ĭ-kəl) adj.Related Videos:
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albite
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Common feldspar mineral, a sodium aluminosilicate (NaAlSi3O8) that occurs most widely in pegmatites and acid igneous rocks such as granites. It may also be found in low-grade metamorphic rocks (those formed under relatively low temperature and pressure conditions) and in certain sedimentary rocks. Albite usually forms brittle, glassy crystals that may be colourless, white, yellow, pink, green, or black. It is used in the manufacture of glass and ceramics, but its primary geologic importance is as a rock-forming mineral.
For more information on albite, visit Britannica.com.
A sodium-rich plagioclase feldspar mineral whose composition extends over the range Ab100An0 to Ab90An10, where Ab (= albite) is NaAlSi3O8 and An (= anorthite) is CaAl2Si2O8. Albite occurs in crustal igneous rocks as a major component of pegmatites and granites, in association with quartz, mica (usually muscovite), and potassium feldspar (orthoclase or microcline). Sodium and potassium feldspars usually occur as distinct mineral grains, sizes varying from millimeter to meter scale. They are frequently intergrown; if the intergrowth is visually observable in a hand specimen, the composite material is known as macroperthite; if visible only in a microscope, microperthite; and if submicroscopic in scale, cryptoperthite. In metamorphic rocks albite is found in granitic gneisses, and it may be the principal component of arkose, a feldspar-dominant, sedimentary rock. Cleavelandite, a platy variety, is sometimes found in lithium-rich pegmatites. See also Arkose; Feldspar; Gneiss; Igneous rocks; Pegmatite; Perthite.
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Albite
| Albite | |
|---|---|
_Island,_Greece.jpg) Albite from Crete, scale = 1 in. |
|
| General | |
| Category | plagioclase, feldspar, tectosilicate |
| Chemical formula | NaAlSi3O8 or Na1.0–0.9Ca0.0–0.1Al1.0–1.1Si3.0–2.9O8 |
| Crystal symmetry | Triclinic H–M Symbol 1 |
| Unit cell | a = 8.16 Å, b = 12.87 Å, c = 7.11 Å; α = 93.45°, β = 116.4°, γ = 90.28°; Z=4 |
| Identification | |
| Color | White to gray, blueish, greenish, reddish; may be chatoyant |
| Crystal habit | Crystals commonly tabular, divergent aggregates, granular, cleavable massive |
| Crystal system | Triclinic Pinacoidal |
| Twinning | Coomon giving polysynthetic striae on {001} or {010}also contact, simple and multiple |
| Cleavage | Perfect on {001}, very good on {010}, imperfect on {110} |
| Fracture | Uneven to conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 6 – 6.5 |
| Luster | Vitreous, typically pearly on cleavages |
| Streak | White |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 2.60 - 2.65 |
| Optical properties | Biaxial (+) |
| Refractive index | nα = 1.528 – 1.533 nβ = 1.532 – 1.537 nγ = 1.538 – 1.542 |
| Birefringence | δ = 0.010 |
| 2V angle | 85–90° (low); 52–54° (high) |
| Dispersion | r < v weak |
| Other characteristics | Low- and high-temperature structural modifications are recognized |
| References | [1][2][3] |
Albite is a felsic plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. As such it represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula NaAlSi3O8. It is a tectosilicate. Its color is usually pure white, hence its name from Latin albus.
Albite crystallizes with triclinic pinacoidal forms. Its specific gravity is about 2.62 and it has a Mohs hardness of 6 - 6.5. Albite almost always exhibits crystal twinning often as minute parallel striations on the crystal face. Albite often occurs as fine parallel segregations alternating with pink microcline in perthite as a result of exolution on cooling.
It occurs in granitic and pegmatite masses, in some hydrothermal vein deposits and forms part of the typical greenschist metamorphic facies for rocks of originally basaltic composition.
It was first reported in 1815 for an occurrence in Finnbo, Falun, Dalarna, Sweden. The name is from Latin, albus for the typical white color.[2]
References
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Wikimedia Commons has media related to: Albite |
- ^ http://rruff.geo.arizona.edu/doclib/hom/albite.pdf Handbook of Mineralogy
- ^ a b http://www.mindat.org/min-96.html Mindat.org
- ^ http://www.webmineral.com/data/Albite.shtml Webmineral data
- Mineral galleries
This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). Encyclopædia Britannica (11th ed.). Cambridge University Press.
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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.
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Britannica Concise Encyclopedia. © 1994-2012 Encyclopædia Britannica, Inc. All rights reserved. Read more
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