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Orthoclase

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Formula:
K(AlSi3O8)
Colour:
Colorless to white, Greenish white, Grayish yellow, Pale pink
Lustre:
Vitreous, Sub-Vitreous, Resinous
Hardness:
6
Specific Gravity:
2.55 - 2.63
Crystal System:
Monoclinic
Member of:
Name:
Named "orthose" in 1801 by Rene Just Haüy from the Greek orthos - "right" 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 orthoklas 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.
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Classification of OrthoclaseHide

Approved, 'Grandfathered' (first described prior to 1959)
9.FA.30

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

76 : TECTOSILICATES Al-Si Framework
1 : Al-Si Framework with Al-Si frameworks
16.3.6

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

Pronounciation of OrthoclaseHide

Pronounciation:
PlayRecorded byCountry
Jolyon & Katya RalphUnited Kingdom

Physical Properties of OrthoclaseHide

Vitreous, Sub-Vitreous, Resinous
Transparency:
Transparent, Translucent
Comment:
Slightly pearly on cleavage
Colour:
Colorless to white, Greenish white, Grayish yellow, Pale pink
Streak:
White
Hardness:
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:
2.55 - 2.63 g/cm3 (Measured)    2.563 g/cm3 (Calculated)

Optical Data of OrthoclaseHide

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
Max Birefringence:
δ = 0.004 - 0.005
Image 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 OrthoclaseHide

Formula:
K(AlSi3O8)
IMA Formula:
KAlSi3O8
Common Impurities:
Na,Fe,Ba,Rb,Ca

Crystallography of OrthoclaseHide

Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Space Group:
B2/m
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 V:
724.57 ų
Z:
4
Morphology:
Short prismatic
Twinning:
Common as Carlsbad, Baveno and Manebach.

Crystallographic forms of OrthoclaseHide

Crystal Atlas:
Image Loading
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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)
3d models and HTML5 code kindly provided by www.smorf.nl.

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X-Ray Powder DiffractionHide

Image Loading

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

Synonyms of OrthoclaseHide

Other Language Names for OrthoclaseHide

Varieties of OrthoclaseHide

AglauriteA variety of Orthoclase feldspar with a blue reflection.
Originally described from Teplice (Teplitz), Ústí Region, Bohemia (Böhmen; Boehmen), Czech Republic.
Arsenian OrthoclaseAs-bearing orthoclase variety from Tolbachik volcano (Arsenatnaya and Yadovitaya fumaroles). Compare filatovite.
Barian Orthoclase
DelawaritePearly

Relationship of Orthoclase to other SpeciesHide

Member of:
Other Members of this group:
AlbiteNa(AlSi3O8)Tric. 1
AmazoniteK(AlSi3O8)
Andesine(Na,Ca)[Al(Si,Al)Si2O8]Tric.
AnorthiteCa(Al2Si2O8)Tric. 1 : P1
Anorthoclase(Na,K)AlSi3O8Tric.
BanalsiteNa2BaAl4Si4O16Orth.
Buddingtonite(NH4)(AlSi3)O8Mon. 2 : P21
Bytownite(Ca,Na)[Al(Al,Si)Si2O8]Tric.
CelsianBa(Al2Si2O8)Mon. 2/m
DmisteinbergiteCa(Al2Si2O8)Hex. 6/mmm (6/m 2/m 2/m) : P6/mmm
FilatoviteK(Al,Zn)2(As,Si)2O8Mon. 2/m
HexacelsianBaAl2Si2O8Hex. 6/mmm (6/m 2/m 2/m) : P63/mcm
Hyalophane(K,Ba)[Al(Si,Al)Si2O8]Mon.
KokchetaviteK(AlSi3O8)Hex. 6/mmm (6/m 2/m 2/m) : P6/mmm
KumdykoliteNa(AlSi3O8)Orth. mmm (2/m 2/m 2/m) : Pnnm
Labradorite(Ca,Na)[Al(Al,Si)Si2O8]
MicroclineK(AlSi3O8)Tric. 1
Oligoclase(Na,Ca)[Al(Si,Al)Si2O8]
ParacelsianBa(Al2Si2O8)Mon.
ReedmergneriteNaBSi3O8Tric.
RubiclineRb(AlSi3O8)Tric.
SanidineK(AlSi3O8)Mon. 2/m : B2/m
SlawsoniteSr(Al2Si2O8)Mon.
StronalsiteNa2SrAl4Si4O16Orth.
SunstoneA variety of feldspar (microcline or oligoclase, more rarely labradorite) that has schiller, ...
SvyatoslaviteCa(Al2Si2O8)Orth.
Forms a series with:

Common AssociatesHide

AlbiteNa(AlSi3O8)
Amphibole SupergroupAX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
BiotiteA series or subgroup of the Mica Group.
MuscoviteKAl2(AlSi3O10)(OH)2
QuartzSiO2
Associated Minerals Based on Photo Data:
Quartz324 photos of Orthoclase associated with Quartz on mindat.org.
Smoky Quartz233 photos of Orthoclase associated with Smoky Quartz on mindat.org.
Albite135 photos of Orthoclase associated with Albite on mindat.org.
Schorl119 photos of Orthoclase associated with Schorl on mindat.org.
Muscovite109 photos of Orthoclase associated with Muscovite on mindat.org.
Aegirine105 photos of Orthoclase associated with Aegirine on mindat.org.
Fluorite100 photos of Orthoclase associated with Fluorite on mindat.org.
Aquamarine90 photos of Orthoclase associated with Aquamarine on mindat.org.
Spessartine82 photos of Orthoclase associated with Spessartine on mindat.org.
Epidote67 photos of Orthoclase associated with Epidote on mindat.org.

Related Minerals - Nickel-Strunz GroupingHide

9.FA.05KaliophiliteKAlSiO4Hex.
9.FA.05KalsiliteKAlSiO4Hex. 6 2 2 : P63 2 2
9.FA.05Nepheline(Na,K)AlSiO4Hex. 6 : P63
9.FA.05Panunzite(K,Na)AlSiO4Hex. 6 : P63
9.FA.05Trikalsilite(K,Na)AlSiO4Hex.
9.FA.05Yoshiokaite(Ca,Na)[Al(Al,Si)O4]Trig. 3 : P3
9.FA.05MegakalsiliteKAlSiO4Hex.
9.FA.10MalinkoiteNaBSiO4Hex. 6 : P63
9.FA.15VirgiliteLiAlSi2O6Hex. 6 2 2 : P62 2 2
9.FA.25LisitsyniteKBSi2O6Orth. 2 2 2 : P2 2 2
9.FA.30AdulariaKAlSi3O8Mon.
9.FA.30Anorthoclase(Na,K)AlSi3O8Tric.
9.FA.30Buddingtonite(NH4)(AlSi3)O8Mon. 2 : P21
9.FA.30CelsianBa(Al2Si2O8)Mon. 2/m
9.FA.30Hyalophane(K,Ba)[Al(Si,Al)Si2O8]Mon.
9.FA.30MicroclineK(AlSi3O8)Tric. 1
9.FA.30SanidineK(AlSi3O8)Mon. 2/m : B2/m
9.FA.30RubiclineRb(AlSi3O8)Tric.
9.FA.30MonalbiteNaAlSi3O8Mon. 2/m : B2/m
9.FA.35AlbiteNa(AlSi3O8)Tric. 1
9.FA.35Andesine(Na,Ca)[Al(Si,Al)Si2O8]Tric.
9.FA.35AnorthiteCa(Al2Si2O8)Tric. 1 : P1
9.FA.35Bytownite(Ca,Na)[Al(Al,Si)Si2O8]Tric.
9.FA.35Labradorite(Ca,Na)[Al(Al,Si)Si2O8]
9.FA.35Oligoclase(Na,Ca)[Al(Si,Al)Si2O8]
9.FA.35ReedmergneriteNaBSi3O8Tric.
9.FA.40ParacelsianBa(Al2Si2O8)Mon.
9.FA.45SvyatoslaviteCa(Al2Si2O8)Orth.
9.FA.45KumdykoliteNa(AlSi3O8)Orth. mmm (2/m 2/m 2/m) : Pnnm
9.FA.50SlawsoniteSr(Al2Si2O8)Mon.
9.FA.55LisetiteCaNa2Al4Si4O16Orth.
9.FA.60BanalsiteNa2BaAl4Si4O16Orth.
9.FA.60StronalsiteNa2SrAl4Si4O16Orth.
9.FA.65DanburiteCaB2Si2O8Orth. mmm (2/m 2/m 2/m)
9.FA.65MaleeviteBaB2Si2O8Orth. mmm (2/m 2/m 2/m) : Pnma
9.FA.65PekoviteSrB2Si2O8
9.FA.70Lingunite(Na,Ca)AlSi3O8Tet. 4/m : I4/m
9.FA.75KokchetaviteK(AlSi3O8)Hex. 6/mmm (6/m 2/m 2/m) : P6/mmm

Related Minerals - Dana Grouping (8th Ed.)Hide

76.1.1.2SanidineK(AlSi3O8)Mon. 2/m : B2/m
76.1.1.3Hyalophane(K,Ba)[Al(Si,Al)Si2O8]Mon.
76.1.1.4CelsianBa(Al2Si2O8)Mon. 2/m
76.1.1.5MicroclineK(AlSi3O8)Tric. 1
76.1.1.6Anorthoclase(Na,K)AlSi3O8Tric.

Related Minerals - Hey's Chemical Index of Minerals GroupingHide

16.3.1LithositeK6Al4Si8O25 · 2H2OMon.
16.3.2KaliophiliteKAlSiO4Hex.
16.3.3KalsiliteKAlSiO4Hex. 6 2 2 : P63 2 2
16.3.4LeuciteK(AlSi2O6)Tet. 4/m : I41/a
16.3.5MicroclineK(AlSi3O8)Tric. 1
16.3.7SanidineK(AlSi3O8)Mon. 2/m : B2/m
16.3.8MuscoviteKAl2(AlSi3O10)(OH)2Mon. 2/m : B2/b

Fluorescence of OrthoclaseHide

May fluoresce dull white or red in SW UV

Other InformationHide

Health Risks:
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

Orthoclase in petrologyHide

References for OrthoclaseHide

Reference List:
Sort by Year (asc) | by Year (desc) | by Author (A-Z) | by Author (Z-A)
Coombs, D.S. (1954) Ferriferous orthoclase from Madagascar. Mineralogical Magazine: 30: 409-427.
Brace, W.F. and Walsh, J.B. (1962) Some direct measurements of the surface energy of quartz and orthoclase. American Mineralogist: 47: 1111-1122.
Wright, T.L., 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., 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.
(1977) Mineralogical Record: 8: 363.
Eggleton, R.A., 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., 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., 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., 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., 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., 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 OrthoclaseHide

Localities for OrthoclaseHide

This 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.

Locality ListShow