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Anorthoclase

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Formula:
(Na,K)AlSi3O8
System:
Triclinic
Colour:
white, colourless, ...
Hardness:
6 - 6½
Member of:
Name:
Named in 1885 by Karl Harry Ferdinand Rosenbusch from the Greek αν, ορθός and κλάσις, meaning "not right cleavage", descriptive of the mineral's cleavage.
Polymorph of:
Feldspar Group.
An alkali feldspar intermediate between low sanidine and high albite.
Occurs in high-temperature sodic volcanic and hypabyssal rocks.

Visit gemdat.org for gemological information about Anorthoclase.

Classification of Anorthoclase

Discredited
9.FA.30

9 : SILICATES (Germanates)
F : Tektosilicates without zeolitic H2O
A : Tektosilicates without additional non-tetrahedral anions
76.1.1.6

76 : TECTOSILICATES Al-Si Framework
1 : Al-Si Framework with Al-Si frameworks
16.4.4

16 : Silicates Containing Aluminum and other Metals
4 : Aluminosilicates of Na and K
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First Recorded Occurrence of Anorthoclase

Year of Discovery:
1885

Physical Properties of Anorthoclase

Colour:
white, colourless, greyish pink
Streak:
white
Hardness (Mohs):
6 - 6½
Cleavage:
Perfect

Crystallography of Anorthoclase

Crystal System:
Triclinic
Cell Parameters:
a = 8.28Å, b = 12.97Å, c = 7.15Å
α = 91.05°, β = 116.26°, γ = 90.15°
Ratio:
a:b:c = 0.638 : 1 : 0.551
X-Ray Powder Diffraction:
Image Loading

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

Optical Data of Anorthoclase

Type:
Biaxial (-)
RI values:
nα = 1.519 - 1.529 nβ = 1.524 - 1.534 nγ = 1.527 - 1.536
2V:
Measured: 34° to 60°, Calculated: 64° to 74°
Max Birefringence:
δ = 0.008
Image shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:
Low
Dispersion:
r > v

Chemical Properties of Anorthoclase

Formula:
(Na,K)AlSi3O8
Essential elements:
All elements listed in formula:
Common Impurities:
Fe,Ca

Relationship of Anorthoclase to other Species

Member of:
Other Members of Group:
AlbiteNaAlSi3O8
Amazonite
Andesine(Na,Ca)[Al(Si,Al)Si2O8]
AnorthiteCaAl2Si2O8
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.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.35AnorthiteCaAl2Si2O8
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
16.4.1Nepheline(Na,K)AlSiO4
16.4.2Panunzite(K,Na)AlSiO4
16.4.3Trikalsilite(K,Na)AlSiO4
16.4.5Naujakasite(Na,K)6(Fe2+,Mn2+,Ca)(Al,Fe)4Si8O26
16.4.6Montesommaite(K,Na)9Al9Si23O64 · 10H2O

Other Names for Anorthoclase

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 Anorthoclase

Reference List:
Carmichael, I.S.E. and W.S. MacKenzie (1964) The lattice parameters of high-temperature triclinic sodic feldspars. Mineral. Mag., 33, 949-962.

Harlow, G.E. (1982) The anorthoclase structures: the effects of temperature and composition. Amer. Mineral., 67, 975-996.

Kroll, H. and Knitter, R. (1991) Al, Si exchange kinetics in sanidine and anorthoclase and modeling of rock cooling paths. American Mineralogist: 76: 928-941.

Internet Links for Anorthoclase

Localities for Anorthoclase

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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