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Orthoclase

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Pópulo, Alijó, Vila Real District, Portugal
© Rui Nunes 2006

Show Orthoclase Photos (195)
Formula:
K[AlSi
 
3
O
 
8
]
System:MonoclinicColour:Colorless, Greenish, ...
Hardness:6
Name:From the Greek orthos - "right" and kalo - "I cleave" in allusion to the mineral's right angle of good cleavage.
Dimorph of:Microcline


Feldspar Group. Celsian-Orthoclase Series.

Classification of Orthoclase

IMA status:Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
Strunz 8th edition ID:8/J.06-40
Nickel-Strunz 10th (pending) edition ID:9.FA.30

9 : SILICATES (Germanates)
F : Tektosilicates without zeolitic H2O
A : Tektosilicates without additional non-tetrahedral anions
Dana 7th edition ID:76.1.1.1
Dana 8th edition ID:76.1.1.1

76 : TECTOSILICATES Al-Si Framework
1 : Al-Si Framework with Al-Si frameworks
Hey's CIM Ref.:16.3.6

16 : Silicates Containing Aluminum and other Metals
3 : Aluminosilicates of K
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Occurrences of Orthoclase

Geological Setting:Common feldspar of granites, syenites and high grade metamorphic rocks.

Physical Properties of Orthoclase

Lustre:Vitreous
Diaphaneity (Transparency):Transparent, Translucent
Comment:Pearly on cleavage
Colour:Colorless, Greenish, Grayish yellow, White, Pink
Streak:White
Hardness (Mohs):6
Hardness Data:Mohs hardness reference species
Tenacity:Brittle
Cleavage:Perfect
Perfect on {001}, good on {010}
Parting:On {100} {110} {110} {201}
Fracture:Irregular/Uneven, Conchoidal
Density (measured):2.55 - 2.63 g/cm3
Density (calculated):2.563 g/cm3

Crystallography of Orthoclase

Crystal System:Monoclinic
Class (H-M):2/m - Prismatic
Space Group:B2/m (B1 1 2/m) [C2/m] {C1 2/m 1}
Cell Parameters:a = 8.5632(11) Å, b = 12.963(14) Å, c = 7.299(11) Å
β = 116.073(9)°
Ratio:a:b:c = 0.661 : 1 : 0.563
Unit Cell Volume:V 724.57 ų
Z:4
Morphology:Short prismatic
Twinning:Common as Carlsbad, Baveno and Manebach.
Crystal Atlas:
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Click on an icon to view
Orthoclase no.49 - Goldschmidt (1913-1926)
Orthoclase no.50 - Goldschmidt (1913-1926)
Orthoclase no.58 - Goldschmidt (1913-1926)
Orthoclase no.64 - Goldschmidt (1913-1926)
Orthoclase no.65 - Goldschmidt (1913-1926)
Orthoclase no.76 - Goldschmidt (1913-1926)
Orthoclase no.145 - Goldschmidt (1913-1926)
Orthoclase no.174 - Goldschmidt (1913-1926)
Orthoclase no.410 - Goldschmidt (1913-1926)
Orthoclase no.434 - Goldschmidt (1913-1926)
Orthoclase no.460 - Goldschmidt (1913-1926)

About Crystal Atlas

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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: Peaks:
Data courtesy of RRUFF project at University of Arizona, used with permission.

Optical Data of Orthoclase

Type:Biaxial (-)
RI values: nα = 1.518 - 1.520 nβ = 1.522 - 1.524 nγ = 1.522 - 1.525
2V:Measured: 35° to 75°, Calculated: 52° to 70°
Maximum Birefringence:δ = 0.004 - 0.005

Chart shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:Low
Dispersion:r > v distinct

Chemical Properties of Orthoclase

Formula:
K[AlSi
 
3
O
 
8
]
Essential elements:Al, K, O, Si
All elements listed in formula:Al, K, O, Si
Common Impurities:Na,Fe,Ba,Rb,Ca

Relationship of Orthoclase to other Species

Series:Forms a series with Hyalophane (see here)
Forms a series with Celsian (see here)
Common Associates:
SchorlQuartzMuscoviteBiotiteBeryl
Albite
Related Minerals - Nickel-Strunz Grouping):
9.FA.IMA2007-049
NaAlSi
 
3
O
 
8
9.FA.05Kaliophilite
K[AlSiO
 
4
]
9.FA.05Kalsilite
K[AlSiO
 
4
]
9.FA.05Nepheline
(Na,K)[AlSiO
 
4
]
9.FA.05Panunzite
(Na,K)[AlSiO
 
4
]
9.FA.05Trikalsilite
(Na,K)[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
Ba[Al
 
2
Si
 
2
O
 
8
]
9.FA.30Hyalophane
(K,Ba)[Al(Si,Al)Si
 
2
O
 
8
]
9.FA.30Microcline
K[AlSi
 
3
O
 
8
]
9.FA.30Sanidine
K[AlSi
 
3
O
 
8
]
9.FA.30Rubicline
(Rb,K)[AlSi
 
3
O
 
8
]
9.FA.30Kokchetavite
KAlSi
 
3
O
 
8
9.FA.30Monalbite
Na[AlSi
 
3
O
 
8
]
9.FA.35Albite
Na[AlSi
 
3
O
 
8
]
9.FA.35Andesine
(Na,Ca)[Al(Si,Al)Si
 
2
O
 
8
]
9.FA.35Anorthite
Ca[Al
 
2
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.35Lingunite
(Na,Ca)AlSi
 
3
O
 
8
9.FA.40Paracelsian
Ba[Al
 
2
Si
 
2
O
 
8
]
9.FA.45Svyatoslavite
Ca[Al
 
2
Si
 
2
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
Ca[BSiO
 
4
]
 
2
9.FA.65Maleevite
BaB
 
2
Si
 
2
O
 
8
9.FA.65Pekovite
SrB
 
2
Si
 
2
O
 
8
Related Minerals - Hey's Index Grouping:
16.3.1Lithosite
K
 
6
Al
 
4
Si
 
8
O
 
25
·2H
 
2
O
16.3.2Kaliophilite
K[AlSiO
 
4
]
16.3.3Kalsilite
K[AlSiO
 
4
]
16.3.4Leucite
KAlSi
 
2
O
 
6
16.3.5Microcline
K[AlSi
 
3
O
 
8
]
16.3.7Sanidine
K[AlSi
 
3
O
 
8
]
16.3.8Muscovite
KAl
 
2
[(OH)
 
2
|AlSi
 
3
O
 
10
]

Other Names for Orthoclase

Synonyms:
ArgillyiteCommon FeldsparCottaiteLeeliteMuldan
Murchisonite
Bulgarian names:
Ортоклаз
Croatian names:
Ortoklas
Dutch names:
Orthoklaas
French names:
Orthose
German names:
OrthoklasAglairitArgillyitCottaitLeelit
Murchisonit
Hebrew names:
אורתוקלז
Italian names:
OrtoclasioOrtose
Polish names:
Ortoklaz
Portuguese names:
Ortoclase
Russian names:
Ортоклаз
Serbian (Cyrillic Script) names:
Ортоклаз
Slovak names:
Ortoklas
Spanish names:
OrtoclasaArgillyitaCottaitaLeelitaMurchisonita
Swedish names:
Ortoklas
Varieties:
AdulariaAglauriteBarian OrthoclaseBarium-AdulariaGermanium-orthoclase
Valencianite

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.
Industrial Uses:Ceramics

References for Orthoclase

Reference List:Coombs, D.S. (1954) Ferriferous orthoclase from Madagascar. Mineralogical Magazine: 30: 409-427.

Prince, E., Donnay, G., and Martin, R.F. (1973) Neutron diffraction refinement of an ordered orthoclase structure. American Mineralogist: 58: 500-507.

Foland, K.A. (1974) 40Ar diffusion in homogeneous orthoclase and an interpretation of Ar diffusion in K-feldspar. Geochimica et Cosmochimica Acta: 3: 151-166.

Mineralogical Record (1977): 8: 363.

Eggleton, R.A. and Buseck, P.R. (1980) The orthoclase-microcline inversion: A high resolution transmission electron microscope study and strain analysis. Contributions to Mineralogy and Petrology: 74: 123-133.

Priess, U. (1981) Untersuchungen zur Tief-Hoch-Umwandlung von Fe-haltingen Orthoklas-Kristallen aus Madagaskar. Neues Jahrbuch für Mineralogie, Abhandlungen: 141: 17-29.

Goldsmith, J. (1988) Enhanced Al/Si diffusion in KAlSi3O8 at high pressures: the effect of hydrogen. Journal of Geology: 96: 109-124.

Foland, K.A. and Xu, Y.-P. (1990) Diffusion of 40Ar and 39Ar in irradiated orthoclase. Geochimica et Cosmochimica Acta: 54: 3147-3158.

Widder, W. (1991) Röntgentopographische Untersuchungen am Sanidin von Volkesfeld und Orthoklas von Madagaskar. Diplomarbeit an der Fakultät für Physik, Universität Karlsruhe, Karlsruhe, Germany.

Waldron, K.A., Parsons, I., and Brown, W.L. (1993) Solution-redeposition and the orthoclase-microcline transformation: evidence from granulites and relevance to 18O exchange. Mineralogical Magazine: 57: 687-695.

Acta Crystallographica (1995): A53.

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: 606.

Kimata, M., Saito, S., Shimizu, M., Iida, I., and Tomoaki, M. (1996) Low-temperature crystal structures of orthoclase and sanidine. Neues Jahrbuch für Mineralogie, Abhandlungen: 171: 199-213.

Villa, I.M. (1996) The influence of irradiation and heating schedule on Ar diffusion in gem-quality orthoclase from Madagascar. Journal Conf. Abstr.: 1(1): 652.

Arnaud, N.O. and Kelley, S.P. (1997) Argon behaviour in gem-quality orthoclase from Madagascar: experiments and some consequences for 40Ar/39Ar geochronology. Geochimica et Cosmochimica Acta: 61: 3227-3255.

Fenter, P., Teng, H., Geissbühler, P., Hanchar, J.M., Nagy, K., and Sturchio, N.C. (2000) Atomic-scale structure of the orthoclase (001) - water interface measured with high-resolution X-ray reflectivity. Geochimica et Cosmochimica Acta: 64: 3663-3673.

Teng, H.H., Fenter, P., Cheng, L., and Sturchio, N.C. (2001) Resolving orthoclase dissolution processes with atomic force microscopy and X-ray reflectivity. Geochimica et Cosmochimica Acta: 65: 3459-3474.

Internet Links for Orthoclase

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    Localities for Orthoclase

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