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Anorthite

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Formula:
CaAl
 
2
Si
 
2
O
 
8
System:TriclinicColour:Colourless, reddish ...
Hardness:6 - 6½
Member of:Feldspar Group
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.
Polymorph of:Dmisteinbergite, Svyatoslavite


Feldspar Group.

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

High- and low-temperature structural modifications exist.

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Classification of Anorthite

IMA status:Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
Strunz 8th edition ID:8/J.07-70
Nickel-Strunz 10th (pending) edition ID:9.FA.35

9 : SILICATES (Germanates)
F : Tektosilicates without zeolitic H2O
A : Tektosilicates without additional non-tetrahedral anions
Hey's CIM Ref.:16.9.2

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

Type Locality:Monte Somma, Somma-Vesuvius Complex, Naples Province, Campania, Italy
Year of Discovery:1823

Occurrences of Anorthite

Geological Setting:Mafic plutonic rocks

Physical Properties of Anorthite

Lustre: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 (measured):2.74 - 2.76 g/cm3
Density (calculated):2.76 g/cm3

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
Unit Cell Volume:V 1,337.25 ų (Calculated from Unit Cell)
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°)
Crystal Atlas:
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Anorthite no.89 - Goldschmidt (1913-1926)
Anorthite no.126 - Goldschmidt (1913-1926)

About Crystal Atlas

The mindat.org Crystal Atlas allows you to view a selection of crystal drawings of real and idealised crystal forms for this mineral and, in certain cases, 3d rotating crystal objects. The 3d models and HTML5 code are kindly provided by www.smorf.nl.

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X-Ray Powder Diffraction:
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Radiation - Copper Kα
Data Set:
Horizontal Axis: ° to ° Vertical Axis: % Source Data: Filtered Data:
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°
Maximum Birefringence:δ = 0.012 - 0.013

Chart 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:
CaAl
 
2
Si
 
2
O
 
8
Simplified for copy/paste:CaAl2Si2O8
Essential elements:Al, Ca, O, Si
All elements listed in formula:Al, Ca, O, Si
Common Impurities:Ti,Fe,Na,K

Relationship of Anorthite to other Species

Series:Forms a series with Albite (see here)
Member of:Feldspar Group
Other Members of Group:

- +
Albite
NaAlSi
 
3
O
 
8
Amazonite
Andesine
(Na,Ca)[Al(Si,Al)Si
 
2
O
 
8
]
Anorthoclase
(Na,K)AlSi
 
3
O
 
8
Banalsite
BaNa
 
2
[Al
 
2
Si
 
2
O
 
8
]
 
2
Buddingtonite
(NH
 
4
)AlSi
 
3
O
 
8
Bytownite
(Ca,Na)[Al(Al,Si)Si
 
2
O
 
8
]
Celsian
BaAl
 
2
Si
 
2
O
 
8
Dmisteinbergite
CaAl
 
2
Si
 
2
O
 
8
Hyalophane
(K,Ba)[Al(Si,Al)Si
 
2
O
 
8
]
Labradorite
(Ca,Na)[Al(Al,Si)Si
 
2
O
 
8
]
Microcline
KAlSi
 
3
O
 
8
Oligoclase
(Na,Ca)[Al(Si,Al)Si
 
2
O
 
8
]
Orthoclase
KAlSi
 
3
O
 
8
Paracelsian
BaAl
 
2
Si
 
2
O
 
8
Reedmergnerite
Na[BSi
 
3
O
 
8
]
Sanidine
KAlSi
 
3
O
 
8
Slawsonite
(Sr,Ca)Al
 
2
Si
 
2
O
 
8
Stronalsite
SrNa
 
2
[Al
 
2
Si
 
2
O
 
8
]
 
2
Svyatoslavite
CaAl
 
2
Si
 
2
O
 
8
Related Minerals - Nickel-Strunz Grouping):

- +
9.FA.05Kaliophilite
KAlSiO
 
4
9.FA.05Kalsilite
KAlSiO
 
4
9.FA.05Nepheline
(Na,K)AlSiO
 
4
9.FA.05Panunzite
(K,Na)AlSiO
 
4
9.FA.05Trikalsilite
(K,Na)AlSiO
 
4
9.FA.05Yoshiokaite
(Ca,Na)[Al(Al,Si)O
 
4
]
9.FA.05Megakalsilite
KAlSiO
 
4
9.FA.10Malinkoite
NaBSiO
 
4
9.FA.15Virgilite
LiAlSi
 
2
O
 
6
9.FA.25Lisitsynite
KBSi
 
2
O
 
6
9.FA.30Adularia
KAlSi
 
3
O
 
8
9.FA.30Anorthoclase
(Na,K)AlSi
 
3
O
 
8
9.FA.30Buddingtonite
(NH
 
4
)AlSi
 
3
O
 
8
9.FA.30Celsian
BaAl
 
2
Si
 
2
O
 
8
9.FA.30Hyalophane
(K,Ba)[Al(Si,Al)Si
 
2
O
 
8
]
9.FA.30Microcline
KAlSi
 
3
O
 
8
9.FA.30Orthoclase
KAlSi
 
3
O
 
8
9.FA.30Sanidine
KAlSi
 
3
O
 
8
9.FA.30Rubicline
(Rb,K)AlSi
 
3
O
 
8
9.FA.30Monalbite
NaAlSi
 
3
O
 
8
9.FA.35Albite
NaAlSi
 
3
O
 
8
9.FA.35Andesine
(Na,Ca)[Al(Si,Al)Si
 
2
O
 
8
]
9.FA.35Bytownite
(Ca,Na)[Al(Al,Si)Si
 
2
O
 
8
]
9.FA.35Labradorite
(Ca,Na)[Al(Al,Si)Si
 
2
O
 
8
]
9.FA.35Oligoclase
(Na,Ca)[Al(Si,Al)Si
 
2
O
 
8
]
9.FA.35Reedmergnerite
Na[BSi
 
3
O
 
8
]
9.FA.40Paracelsian
BaAl
 
2
Si
 
2
O
 
8
9.FA.45Svyatoslavite
CaAl
 
2
Si
 
2
O
 
8
9.FA.45Kumdykolite
NaAlSi
 
3
O
 
8
9.FA.50Slawsonite
(Sr,Ca)Al
 
2
Si
 
2
O
 
8
9.FA.55Lisetite
CaNa
 
2
Al
 
4
Si
 
4
O
 
16
9.FA.60Banalsite
BaNa
 
2
[Al
 
2
Si
 
2
O
 
8
]
 
2
9.FA.60Stronalsite
SrNa
 
2
[Al
 
2
Si
 
2
O
 
8
]
 
2
9.FA.65Danburite
CaB
 
2
Si
 
2
O
 
8
9.FA.65Maleevite
BaB
 
2
Si
 
2
O
 
8
9.FA.65Pekovite
SrB
 
2
Si
 
2
O
 
8
9.FA.70Lingunite
(Na,Ca)AlSi
 
3
O
 
8
9.FA.75Kokchetavite
KAlSi
 
3
O
 
8
Related Minerals - Hey's Index Grouping:

- +
16.9.1Gehlenite
Ca
 
2
Al(AlSiO
 
7
)
16.9.3Yoshiokaite
(Ca,Na)[Al(Al,Si)O
 
4
]
16.9.4Svyatoslavite
CaAl
 
2
Si
 
2
O
 
8
16.9.5Dmisteinbergite
CaAl
 
2
Si
 
2
O
 
8
16.9.6Grossular
Ca
 
3
Al
 
2
(SiO
 
4
)
 
3
16.9.7Vuagnatite
CaAl(SiO
 
4
)(OH)
16.9.8Zoisite
{Ca
 
2
}{Al
 
3
}(Si
 
2
O
 
7
)(SiO
 
4
)O(OH)
16.9.9Clinozoisite
{Ca
 
2
}{Al
 
3
}(Si
 
2
O
 
7
)(SiO
 
4
)O(OH)
16.9.10Prehnite
Ca
 
2
Al
 
2
Si
 
3
O
 
10
(OH)
 
2
16.9.11Kamaishilite
Ca
 
2
(Al
 
2
SiO
 
6
)(OH)
 
2
16.9.12Bicchulite
Ca
 
2
(Al
 
2
SiO
 
6
)(OH)
 
2
16.9.13Margarite
CaAl
 
2
(Al
 
2
Si
 
2
O
 
10
)(OH)
 
2
16.9.14Chantalite
CaAl
 
2
(SiO
 
4
)(OH)
 
4
16.9.15Cebollite
Ca
 
5
Al
 
2
(SiO
 
4
)
 
3
(OH)
 
4
16.9.17Katoite
Ca
 
3
Al
 
2
(SiO
 
4
)
 
3-x
(OH)
 
4x
16.9.18Lawsonite
CaAl
 
2
(Si
 
2
O
 
7
)(OH)
 
2
· H
 
2
O
16.9.19Parthéite
CaAl
 
2
Si
 
2
O
 
8
· 2H
 
2
O
16.9.20Wairakite
Ca(Al
 
2
Si
 
4
O
 
12
) · 2H
 
2
O
16.9.21Vertumnite
Ca
 
4
Al
 
4
Si
 
4
O
 
6
(OH)
 
24
· 3H
 
2
O
16.9.22Scolecite
CaAl
 
2
Si
 
3
O
 
10
· 3H
 
2
O
16.9.23Laumontite
CaAl
 
2
Si
 
4
O
 
12
· 4H
 
2
O
16.9.24Yugawaralite
CaAl
 
2
Si
 
6
O
 
16
· 4H
 
2
O
16.9.25Gismondine-Ca
CaAl
 
2
Si
 
2
O
 
8
· 4H
 
2
O
16.9.26Epistilbite
CaAl
 
2
Si
 
6
O
 
16
· 5H
 
2
O
16.9.27Goosecreekite
Ca[Al
 
2
Si
 
6
O
 
16
] · 5H
 
2
O
16.9.28Cowlesite
CaAl
 
2
Si
 
3
O
 
10
· 6H
 
2
O
16.9.30Stellerite
Ca[Al
 
2
Si
 
7
O
 
18
] · 7H
 
2
O
16.9.31Strätlingite
Ca
 
2
Al
 
2
SiO
 
7
· 8H
 
2
O
16.9.32Amstallite
CaAl(Si,Al)
 
4
O
 
8
(OH)
 
4
· (H
 
2
O,Cl)

Other Names for Anorthite

Synonyms:
AmphodeliteAnorthoîteBarsoviteBasic PlagioclaseBeffanite
BeffoniteBiotineCalciclaseCalcium FeldsparChristianite
CyclopiteDidymoliteIndianiteLatrobiteLepolite
Lime-FeldsparThiorsauite
Other Languages:
Bosnian (Latin Script):Anortit
Dutch:Anorthiet
Finnish:Anortiitti
German:Anorthit
Amphodelit
Anorthoît
Barsovit
Beffanit
Beffonit
Cyclopit
Lepolit
Hebrew:אנורתיט
Italian:Anortite
Japanese:灰長石
Lithuanian:Anortitas
Norwegian (Bokmål):Anortitt
Polish:Anortyt
Portuguese:Anortita
Russian:Анортит
Serbian (Cyrillic Script):Анортит
Simplified Chinese:钙长石
基性斜长石
Spanish:Anortita
Amphodelita
Anorthita
Anorthoîta
Barsovita
Beffanita
Beffonita
Cyclopita
Lepolita
Swedish:Anortit
Ukrainian:Анортит
Varieties:
Barium-Anorthite (of Nockolds and Zies)BytowniteLabradoriteLindsayiteLynx Eye

Other Information

Health Warning: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.

Mindat.org articles about Anorthite

Article entries:
Anorthite and Native BrassAlfredo Petrov

Internet Links for Anorthite

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    Localities for Anorthite

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