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Anorthite

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Formula:
CaAl2Si2O8
System:
Triclinic
Colour:
Colourless, reddish ...
Hardness:
6 - 6½
Member of:
Name:
Named in 1823 by Gustav Rose from the Greek αν and oρθός, "not right angle" or "oblique", in allusion to the oblique triclinic form of the crystals.
Feldspar Group.

Ca-rich end member of the Albite-Anorthite Series.

High- and low-temperature structural modifications exist.

Visit gemdat.org for gemological information about Anorthite.

Classification of Anorthite

Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
9.FA.35

9 : SILICATES (Germanates)
F : Tektosilicates without zeolitic H2O
A : Tektosilicates without additional non-tetrahedral anions
16.9.2

16 : Silicates Containing Aluminum and other Metals
9 : Aluminosilicates of Ca
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Type Occurrence of Anorthite

Year of Discovery:
1823

Occurrences of Anorthite

Geological Setting:
Mafic plutonic rocks

Physical Properties of Anorthite

Vitreous
Diaphaneity (Transparency):
Transparent, Translucent
Colour:
Colourless, reddish grey, white
Streak:
White
Hardness (Mohs):
6 - 6½
Tenacity:
Brittle
Cleavage:
Perfect
Perfect on {001}, less so on {010}, imperfect on {110}
Fracture:
Irregular/Uneven, Conchoidal
Density:
2.74 - 2.76 g/cm3 (Measured)    2.76 g/cm3 (Calculated)

Crystallography of Anorthite

Crystal System:
Triclinic
Class (H-M):
1 - Pinacoidal
Space Group:
P1
Cell Parameters:
a = 8.1768Å, b = 12.8768Å, c = 14.169Å
α = 93.17°, β = 115.85°, γ = 92.22°
Ratio:
a:b:c = 0.635 : 1 : 1.1
Z:
8
Morphology:
Commonly short, prismatic, lamellar, coarse granular, massive
Twinning:
Commonly polysynthetic on albite law, pericline, Carlsbad, Manebach and Baveno twinning.
Comment:
Low modification; non-standard unit cell (reduced cell: 8.18, 12.87, 12.90 A, 85.8, 81.1, 88.7°)

Crystallographic forms of Anorthite

Crystal Atlas:
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Anorthite no.89 - Goldschmidt (1913-1926)
Anorthite no.126 - Goldschmidt (1913-1926)
3d models and HTML5 code kindly provided by www.smorf.nl.

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Transparency
Opaque | Translucent | Transparent

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X-Ray Powder Diffraction:
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Radiation - Copper Kα
Data Set:
Data courtesy of RRUFF project at University of Arizona, used with permission.

Optical Data of Anorthite

Type:
Biaxial (-)
RI values:
nα = 1.573 - 1.577 nβ = 1.580 - 1.585 nγ = 1.585 - 1.590
2V:
Measured: 78° to 83°, Calculated: 78°
Max Birefringence:
δ = 0.012 - 0.013
Image shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:
Moderate
Dispersion:
r < v weak

Chemical Properties of Anorthite

Formula:
CaAl2Si2O8
Essential elements:
All elements listed in formula:
Common Impurities:
Ti,Fe,Na,K

Relationship of Anorthite to other Species

Series:
Forms a series with Albite (see here)
Member of:
Other Members of Group:
AlbiteNaAlSi3O8
Amazonite
Andesine(Na,Ca)[Al(Si,Al)Si2O8]
Anorthoclase(Na,K)AlSi3O8
BanalsiteBaNa2[Al2Si2O8]2
Buddingtonite(NH4)AlSi3O8
Bytownite(Ca,Na)[Al(Al,Si)Si2O8]
CelsianBaAl2Si2O8
DmisteinbergiteCaAl2Si2O8
Hyalophane(K,Ba)[Al(Si,Al)Si2O8]
Labradorite(Ca,Na)[Al(Al,Si)Si2O8]
MicroclineKAlSi3O8
Oligoclase(Na,Ca)[Al(Si,Al)Si2O8]
OrthoclaseKAlSi3O8
ParacelsianBaAl2Si2O8
ReedmergneriteNa[BSi3O8]
SanidineKAlSi3O8
Slawsonite(Sr,Ca)Al2Si2O8
StronalsiteSrNa2[Al2Si2O8]2
SvyatoslaviteCaAl2Si2O8
9.FA.05KaliophiliteKAlSiO4
9.FA.05KalsiliteKAlSiO4
9.FA.05Nepheline(Na,K)AlSiO4
9.FA.05Panunzite(K,Na)AlSiO4
9.FA.05Trikalsilite(K,Na)AlSiO4
9.FA.05Yoshiokaite(Ca,Na)[Al(Al,Si)O4]
9.FA.05MegakalsiliteKAlSiO4
9.FA.10MalinkoiteNaBSiO4
9.FA.15VirgiliteLiAlSi2O6
9.FA.25LisitsyniteKBSi2O6
9.FA.30AdulariaKAlSi3O8
9.FA.30Anorthoclase(Na,K)AlSi3O8
9.FA.30Buddingtonite(NH4)AlSi3O8
9.FA.30CelsianBaAl2Si2O8
9.FA.30Hyalophane(K,Ba)[Al(Si,Al)Si2O8]
9.FA.30MicroclineKAlSi3O8
9.FA.30OrthoclaseKAlSi3O8
9.FA.30SanidineKAlSi3O8
9.FA.30Rubicline(Rb,K)AlSi3O8
9.FA.30MonalbiteNaAlSi3O8
9.FA.35AlbiteNaAlSi3O8
9.FA.35Andesine(Na,Ca)[Al(Si,Al)Si2O8]
9.FA.35Bytownite(Ca,Na)[Al(Al,Si)Si2O8]
9.FA.35Labradorite(Ca,Na)[Al(Al,Si)Si2O8]
9.FA.35Oligoclase(Na,Ca)[Al(Si,Al)Si2O8]
9.FA.35ReedmergneriteNa[BSi3O8]
9.FA.40ParacelsianBaAl2Si2O8
9.FA.45SvyatoslaviteCaAl2Si2O8
9.FA.45KumdykoliteNaAlSi3O8
9.FA.50Slawsonite(Sr,Ca)Al2Si2O8
9.FA.55LisetiteCaNa2Al4Si4O16
9.FA.60BanalsiteBaNa2[Al2Si2O8]2
9.FA.60StronalsiteSrNa2[Al2Si2O8]2
9.FA.65DanburiteCaB2Si2O8
9.FA.65MaleeviteBaB2Si2O8
9.FA.65PekoviteSrB2Si2O8
9.FA.70Lingunite(Na,Ca)AlSi3O8
9.FA.75KokchetaviteKAlSi3O8
16.9.1GehleniteCa2Al(AlSiO7)
16.9.3Yoshiokaite(Ca,Na)[Al(Al,Si)O4]
16.9.4SvyatoslaviteCaAl2Si2O8
16.9.5DmisteinbergiteCaAl2Si2O8
16.9.6GrossularCa3Al2(SiO4)3
16.9.7VuagnatiteCaAl(SiO4)(OH)
16.9.8Zoisite{Ca2}{Al3}(Si2O7)(SiO4)O(OH)
16.9.9Clinozoisite{Ca2}{Al3}(Si2O7)(SiO4)O(OH)
16.9.10PrehniteCa2Al2Si3O10(OH)2
16.9.11KamaishiliteCa2(Al2SiO6)(OH)2
16.9.12BicchuliteCa2(Al2SiO6)(OH)2
16.9.13MargariteCaAl2(Al2Si2O10)(OH)2
16.9.14ChantaliteCaAl2(SiO4)(OH)4
16.9.15CebolliteCa5Al2(SiO4)3(OH)4
16.9.17KatoiteCa3Al2(SiO4)3-x(OH)4x
16.9.18LawsoniteCaAl2(Si2O7)(OH)2 · H2O
16.9.19ParthéiteCa2(Si4Al4) O15 (OH)2•4H2O
16.9.20WairakiteCa(Al2Si4O12) · 2H2O
16.9.21VertumniteCa4Al4Si4O6(OH)24 · 3H2O
16.9.22ScoleciteCaAl2Si3O10 · 3H2O
16.9.23LaumontiteCaAl2Si4O12 · 4H2O
16.9.24YugawaraliteCaAl2Si6O16 · 4H2O
16.9.25Gismondine-CaCaAl2Si2O8 · 4H2O
16.9.26EpistilbiteCaAl2Si6O16 · 5H2O
16.9.27GoosecreekiteCa[Al2Si6O16] · 5H2O
16.9.28CowlesiteCaAl2Si3O10 · 6H2O
16.9.30StelleriteCa4(Si28Al8)O72 · 28H2O
16.9.31SträtlingiteCa2Al2SiO7 · 8H2O
16.9.32AmstalliteCaAl(Si,Al)4O8(OH)4 · (H2O,Cl)

Other Names for Anorthite

Name in Other Languages:

Other Information

Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

References for Anorthite

Reference List:
Rose. G. (1823): Über den Feldspat, Albit, Labradorit und Anorthit, Annalen der Physik und Chemie, Vol. 73/NF-43, 175-208.

Acta Crystallographica: 15: 117-135.

Richet, P. and Bottinga, Y. (1984b) Anorthite, andesine, wollastonite, diopside, cordierite, and pyrope thermodynamics of melting, glass transitions, and properties of the amorphous phases. Earth and Planetary Science Letters: 67: 415-432.

Redfern, S.A.T. and Salje, E. (1987), Thermodynamics of plagioclase II: temperature evolution of the spontaneous strain at the I1‾ ↔ P1‾ phase transition in anorthite. Physics and Chemistry of Minerals: 14: 189-195.

Salje, E. (1987), Thermodynamics of plagioclase I: theory of the I1‾ - P1‾ phase transition in anorthite and Ca-rich plagioclases. Physics and Chemistry of Minerals: 14: 181-188.

Angel, R.J. (1988), High-pressure structure of anorthite. American Mineralogist: 73: 1114-1119.

Ghose, S., Van Tendeloo, G., and Amelinkx, S. (1988), Dynamics of a second-order phase transition: P1‾ to I1‾ phase transition in anorthite, CaAl2Si2O8. Science: 242: 1539-1541.

Angel, R.J., Redfern, S.A.T., and Ross, N.L. (1989), Spontaneous strain below the I1‾ - P1‾ transition in anorthite at pressure. Physics and Chemistry of Minerals: 16: 539-544.

Van Tendeloo, G., ose, S., and Amelinckx, S. (1989) A dynamical model for the P1‾ - I1‾ phase transition in anorthite, CaAl2Si2O8 I: Evidence from electron microscopy. Physics and Chemistry of Minerals: 16: 311-319.

Angel, R.J., Carpenter, M.A., and Finger, L.W. (1990), Structural variation associated with compositional variation and order-disorder behaviour in anorthite-rich feldspars. American Mineralogist: 75: 150-162.

Carpenter, M.A., Angel, R.J., and Finger, L.W. (1990), Calibration of Al/Si order variations in anorthite. Contributions to Mineralogy and Petrology: 104: 471-480.

Carpenter, M.A. (1991), Mechanisms and kinetics of Al-Si ordering in anorthite: I. Incommensurate structure and domain coarsening: American Mineralogist: 76: 1110-1119.

Angel, R.J. (1992), Order-disorder and the high-pressure P1‾-I1‾ transition in anorthite. American Mineralogist: 77: 923-929.

Knoche, R., Dingwell, D.B., and Webb, S.L. (1992a) Non-linear temperature dependence of liquid volumes in the system albite-anorthite-diopside. Contributions to Mineralogy and Petrology: 111: 61-73.

Knoche, R., Dingwell, D.B., and Webb, S.L. (1992b) Temperature-dependent thermal expansivities of silicate melts: The system anorthite-diopside. Geochimica et Cosmochimica Acta: 56: 689-699.

Redfern, S.A.T. and Salje, E. (1992), Microscopic dynamic and macroscopic thermodynamic character of the I1‾ - P1‾ phase transition in anorthite Physics and Chemistry of Minerals: 18: 526-533.

Courtial, P., Téqui, C., and Richet, P. (2000) Thermodynamics of diopside, anorthite, pseudowollastonite, CaMgGeO4 olivine, and åkermanite up to near the melting point. Physics and Chemistry of Minerals: 27: 242-250.

Anthony, J.W., Bideaux, R.A., Bladh, K.W., and Nichols, M.C. (1995) Handbook of Mineralogy, Volume II. Silica, Silicates. Mineral Data Publishing, Tucson, AZ, 904pp., 2 sub-volumes: 33.

Internet Links for Anorthite

Specimens:
The following Anorthite specimens are currently listed for sale on minfind.com.

Localities for Anorthite

map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.
Mineral and/or Locality  
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