Orthoclase Mineral Data

Orthoclase Mineral Data +

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General Orthoclase Information

Chemical Formula:

KAlSi3O8

Composition:

Molecular Weight = 278.33 gm

Potassium 14.05 % K 16.92 % K₂O

Aluminum 9.69 % Al 18.32 % Al₂O₃

Silicon 30.27 % Si 64.76 % SiO₂

Oxygen 45.99 % O

______ ______

100.00 % 100.00 % = TOTAL OXIDE

Empirical Formula:

KAlSi₃O₈

Environment:

Intrusive and extrusive igneous, and metamorphic rocks.

IMA Status:

Valid Species (Pre-IMA) 1823

Locality:

Common world wide occurrences. Link to MinDat.org Location Data.

Name Origin:

From the Greek orthos - "right" and kalo -" I cleave" in allusion to the mineral's right angle of good cleavage.

Synonym:

Adularia

Orthose

Orthoclase Image

Images:

Orthoclase Lorenzenite

Comments: Striated, dark violet crystal of lorenzenite in cream-colored orthoclase.
Location: Khibiny Massif, Kola Peninsula, Russia. Scale: 1.3 x 1.2 cm.
© John Veevaert

Images:

Orthoclase

Comments: Carlsbad twinned crystal of orthoclase. Former Mart?n Oliete Fontela collection.
Location: Zarzalejo, Madrid. Scale: 5.2x4.6x2.2 cm.
© Fabre Minerals

Images:

Orthoclase

Comments: Gemmy, twinned adularia (orthoclase) specimen on matrix. Former Bally Museum collection.
Location: Rhonegletscher, Switzerland. Scale: Crystal size 3 x 2 cm.
© Fabre Minerals

Orthoclase Crystallography

Axial Ratios:

a:b:c =0.6636:1:0.5534

Cell Dimensions:

a = 8.625, b = 12.996, c = 7.193, Z = 4; beta = 116.016° V = 724.57 Den(Calc)= 2.55

Crystal System:

Monoclinic - PrismaticH-M Symbol (2/m) Space Group: C 2/m

$Help on X Ray Diffraction:$ X Ray Diffraction:

By Intensity(I/I_o): 3.18(1), 4.02(0.9), 3.8(0.8),

Forms:

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Forms: [ 1 1 0] [ 1 0 1] [ 0 0 1] [ 0 1 0]

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Crystal Structure:

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Colville A A , Ribbe P H , American Mineralogist , 53 (1968) p.25-37, The crystal structure of an adularia and a refinement of the structure of, orthoclase, Note: Spencer B, variety adularia

View Additional jPOWD Structure files for Orthoclase
[1] [2] [3] [4] [5] [6]

Physical Properties of Orthoclase

Cleavage:

[001] Perfect, [010] Good

Color:

Colorless, Greenish, Grayish yellow, White, Pink.

Density:

2.56

Diaphaniety:

Transparent to translucent

Fracture:

Uneven - Flat surfaces (not cleavage) fractured in an uneven pattern.

Habit:

Blocky - Crystal shape tends to be equant (e.g. feldspars).

Habit:

Massive - Granular - Common texture observed in granite and other igneous rock.

Habit:

Prismatic - Crystals Shaped like Slender Prisms (e.g. tourmaline).

Hardness:

6 - Orthoclase

Luminescence:

None.

Luster:

Vitreous (Glassy)

Streak:

white

Optical Properties of Orthoclase

Gladstone-Dale:

CI meas= 0.011 (Superior) - where the CI = (1-KPDmeas/KC)
CI calc= 0.007 (Superior) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.2044,KPDmeas= 0.2036,KC= 0.2058

Optical Data:

Biaxial (-), a=1.518, b=1.522, g=1.523-1.524, bire=0.0050-0.0060, 2V(Calc)=52-70, 2V(Meas)=65-75. Dispersion relatively strong.

Pleochroism (x):

colorless.

Pleochroism (y):

colorless.

Pleochroism (z):

colorless.

Calculated Properties of Orthoclase

Electron Density:

r_electron=2.53 gm/cc
note: r_Orthoclase=2.55 gm/cc.

Fermion Index

Fermion Index = 0.01437
Boson Index = 0.98563

Photoelectric:

PE_Orthoclase= 2.85 barns/electron
U=PE_Orthoclase x r_electron= 7.20 barns/cc.

Radioactivity:

GRapi = 200.97 (Gamma Ray American Petroleum Institute Units)

Estimated Radioactivity from Orthoclase - barely detectable

Orthoclase Classification

Dana Class:

76.1.1.1 (76)Tectosilicate Al-Si Framework

(76.1)with Al-Si frameworks

(76.1.1)K (Na,Ba) feldspars

76.1.1.1 Orthoclase KAlSi3O8 C 2/m 2/m

76.1.1.2 Sanidine (K,Na)(Si,Al)4O8 C 2/m 2/m

76.1.1.3 Hyalophane (K,Ba)Al(Si,Al)3O8 C 2/m 2/m

76.1.1.4 Celsian BaAl2Si2O8 I21/c 2/m

76.1.1.5 Microcline KAlSi3O8 C1 1

76.1.1.6 Anorthoclase (Na,K)AlSi3O8 C1 1

76.1.1.7 Rubicline! (Rb,K)AlSi3O8 P1 1

76.1.1.8 Filatovite! K[(Al,Zn)2(As,Si)2O8] I2/c 2/m

Strunz Class:

VIII/J.06-40 VIII - Silicates

VIII/J - Tectosilicates (network) without anions unfamiliar to the tetraheders

VIII/J.06 - Feldspar group, Buddingtonite - Orthoclase - Slawsonite series

VIII/J.06-10 Buddingtonite (NH4)AlSi3O8·0.5(H2O) P 2₁ or P 2₁/m Mono

VIII/J.06-15 Kokchetavite! KAlSi3O8 P 6/mmm(?) 6/m 2/m 2/m

VIII/J.06-20 Sanidine (K,Na)(Si,Al)4O8 C 2/m 2/m

VIII/J.06-30 Microcline KAlSi3O8 C1 1

VIII/J.06-35 Rubicline! (Rb,K)AlSi3O8 P1 1

VIII/J.06-40 Orthoclase KAlSi3O8 C 2/m 2/m

VIII/J.06-50 Hyalophane (K,Ba)Al(Si,Al)3O8 C 2/m 2/m

VIII/J.06-60 Celsian BaAl2Si2O8 I21/c 2/m

VIII/J.06-70 Paracelsian BaAl2Si2O8 P 2₁/c 2/m

VIII/J.06-80 Slawsonite (Sr,Ca)Al2Si2O8 P 2₁/a 2/m

Other Orthoclase Information

References:

NAME( Duda&Rejl90) PHYS. PROP.(Enc. of Minerals,2nd ed.,1990) OPTIC PROP.(Mason68)

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Orthoclase

KAlSi3O8
Dana No: 76.1.1.1 Strunz No: VIII/J.06-40
Locality:

Notes: