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Orthoclase

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Formula:
KAlSi
 
3
O
 
8
System:MonoclinicColour:Colorless to white, ...
Hardness:6
Member of:Feldspar Group
Name:Named "orthose" in 1801 by Rene Just Haüy from the Greek orthos - "right" and kalo - "I cleave" in allusion to the mineral's right angle of good cleavage. The sense of Haüy's name was that the mineral was a feldspar, but he did not specify a type-locality, nor did Haüy give a chemical analysis. The name was changed in 1823 to orthoklase by Johann Friedrich August Breithaupt. Although petrologists had used twinning as a method of distinguishing orthoclase from microcline, Wright and Stewart (1958) used the difference in certain d values to calculate a degree of disorder of a sample and thus have a quantitative method to identify the structural state of a potassium feldspar. Despite the enormous number of reports of orthoclase in granite pegmatites, orthoclase is extremely rare in such deposits.
Polymorph of:Microcline, Sanidine


Feldspar Group. Celsian-Orthoclase Series.

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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 high temperature granites, syenites, high grade metamorphic rocks, and felsic extrusive rocks.

Physical Properties of Orthoclase

Lustre:Vitreous, Sub-Vitreous, Resinous
Diaphaneity (Transparency):Transparent, Translucent
Comment:Slightly pearly on cleavage
Colour:Colorless to white, Greenish white, Grayish yellow, Pale 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
Space Group Setting:C2/m
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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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

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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Opaque | Translucent | Transparent

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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.
X-Ray Powder Diffraction:
d-spacingIntensity
4.22 (70)
3.77 (80)
3.47 (45)
3.31 (100)
3.29 (60)
3.24 (65)
2.992 (50)
Comments:ICDD 19-931

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°
Birefringence:0.004
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
Optical Extinction:X^a = 6°-14°, Y^c = -13° to 21°, Z = b
Pleochroism:Non-pleochroic

Chemical Properties of Orthoclase

Formula:
KAlSi
 
3
O
 
8
Simplified for copy/paste:KAlSi3O8
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)
Member of:Feldspar Group
Other Members of Group:

- +
Albite
NaAlSi
 
3
O
 
8
Amazonite
Andesine
(Na,Ca)[Al(Si,Al)Si
 
2
O
 
8
]
Anorthite
CaAl
 
2
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
]
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
Common Associates:
QuartzMuscoviteBiotiteAmphibole SupergroupAlbite
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.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.35Anorthite
CaAl
 
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.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:

- +
16.3.1Lithosite
K
 
6
Al
 
4
Si
 
8
O
 
25
· 2H
 
2
O
16.3.2Kaliophilite
KAlSiO
 
4
16.3.3Kalsilite
KAlSiO
 
4
16.3.4Leucite
K(AlSi
 
2
O
 
6
)
16.3.5Microcline
KAlSi
 
3
O
 
8
16.3.7Sanidine
KAlSi
 
3
O
 
8
16.3.8Muscovite
KAl
 
2
(AlSi
 
3
O
 
10
)(OH)
 
2

Other Names for Orthoclase

Synonyms:
ArgillyiteCommon FeldsparCottaiteLeeliteMuldan
MurchisoniteParadoxite
Other Languages:
Bulgarian:Ортоклаз
Croatian:Ortoklas
Dutch:Orthoklaas
French:Orthose
German:Orthoklas
Aglairit
Argillyit
Cottait
Leelit
Murchisonit
Paradoxit
Hebrew:אורתוקלז
Italian:Ortoclasio
Ortose
Japanese:正長石
Korean:정장석
Polish:Ortoklaz
Portuguese:Ortoclase
Russian:Ортоклаз
Serbian (Cyrillic Script):Ортоклаз
Simplified Chinese:正长石
肉红长石
Slovak:Ortoklas
Spanish:Ortoclasa
Argillyita
Cottaita
Leelita
Murchisonita
Swedish:Ortoklas
Traditional Chinese:正長石
肉紅長石
Varieties:
AglauriteBarian OrthoclaseDelawarite

Other Information

Fluorescence in UV light:May fluoresce dull white or red in SW UV
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, abrasives, crushed stone, decorative facing in slabbed rock panels, gem materials

References for Orthoclase

Reference List:

- +
Coombs, D.S. (1954) Ferriferous orthoclase from Madagascar. Mineralogical Magazine: 30: 409-427.
Wright, T. L. and Stewart, D. B. (1968) X-ray and optical study of alkali feldspar, I. Determination of composition and structural state from refined unit-cell parameters and 2Y. American Mineralogist, 53, 38-87
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-haltinge 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

Search Engines:
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  • Look for Orthoclase on Wikipedia
  • Look for Orthoclase on Mineralien Atlas
  • Raman and XRD data at RRUFF project
  • American Mineralogist Crystal Structure Database
  • Orthoclase details from Handbook of Mineralogy (PDF)
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  • Specimens:The following Orthoclase specimens are currently listed for sale on minfind.com.

    Localities for Orthoclase

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