Labradorite Mineral Data

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General Labradorite Information

Chemical Formula:

(Ca,Na)(Si,Al)4O8

Composition:

Molecular Weight = 271.81 gm

Sodium 3.38 % Na 4.56 % Na₂O

Calcium 8.85 % Ca 12.38 % CaO

Aluminum 15.88 % Al 30.01 % Al₂O₃

Silicon 24.80 % Si 53.05 % SiO₂

Oxygen 47.09 % O

______ ______

100.00 % 100.00 % = TOTAL OXIDE

Empirical Formula:

Na_0.4Ca_0.6Al_1.6Si_2.4O₈

Environment:

Magmatic and metamorphic rocks.

IMA Status:

Not Approved IMA 1780

Locality:

Labrador peninsula, Canada. Link to MinDat.org Location Data.

Name Origin:

Named after its locality.

Synonym:

Ab40

An60

Spectrolite

Labradorite Image

Images:

Labradorite Plagioclase

Comments: Dual view of a cleavage fragment of labradorite showing the multi-colored labradorescence (schiller effect) and the same area viewed without the color. The color is due to optical interference on Bøggild exsolution lamellae.
Location: Ihosy, Betroka district, Toliara Province, Madagascar. Scale: Picture size 3x3 cm.
© Dave Barthelmy

Labradorite Crystallography

Axial Ratios:

a:b:c =0.6351:1:0.7912

Cell Dimensions:

a = 8.155, b = 12.84, c = 10.16, Z = 6; alpha = 93.5°, beta = 116.25°, gamma = 89.133° V = 952.25 Den(Calc)= 2.84

Crystal System:

Triclinic - PinacoidalH-M Symbol ( 1) Space Group: C1

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

By Intensity(I/I_o): 3.18(1), 3.21(0.7), 3.76(0.7),

Forms:

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

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Crystal Structure:

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Wenk H R , Joswig W , Tagai T , Korekawa M , Smith B K , American Mineralogist , 65 (1980) p.81-95, The average structure of An 62-66 labradorite, Surtsey x-ray, feldspar

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

Physical Properties of Labradorite

Cleavage:

[001] Perfect, [010] Good, [110] Distinct

Color:

Colorless, Gray, Gray white, White, Light green.

Density:

2.68 - 2.71, Average = 2.69

Diaphaniety:

Translucent to transparent

Fracture:

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

Habit:

Crystalline - Coarse - Occurs as well-formed coarse sized crystals.

Habit:

Granular - Generally occurs as anhedral to subhedral crystals in matrix.

Habit:

Striated - Parallel lines on crystal surface or cleavage face.

Hardness:

7 - Quartz

Luminescence:

Non-fluorescent.

Luster:

Vitreous (Glassy)

Streak:

white

Optical Properties of Labradorite

Gladstone-Dale:

CI meas= -0.009 (Superior) - where the CI = (1-KPDmeas/KC)
CI calc= 0.043 (Good) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.1983,KPDmeas= 0.2089,KC= 0.2071

Optical Data:

Biaxial (+), a=1.554-1.563, b=1.5588-1.5675, g=1.562-1.573, bire=0.0080-0.0100, 2V(Calc)=78-86, 2V(Meas)=85.

Pleochroism (x):

colorless.

Pleochroism (y):

colorless.

Pleochroism (z):

colorless.

Calculated Properties of Labradorite

Electron Density:

r_electron=2.67 gm/cc
note: r_Labradorite=2.70 gm/cc.

Fermion Index

Fermion Index = 0.01192
Boson Index = 0.98808

Photoelectric:

PE_Labradorite= 2.56 barns/electron
U=PE_Labradorite x r_electron= 6.84 barns/cc.

Radioactivity:

GRapi = 0 (Gamma Ray American Petroleum Institute Units)

Labradorite is Not Radioactive

Labradorite Classification

Dana Class:

76.1.3.4 (76)Tectosilicate Al-Si Framework

(76.1)with Al-Si frameworks

(76.1.3)Plagioclase series

76.1.3.0 Plagioclase* (Na,Ca)(Si,Al)4O8 C1 1

76.1.3.1 Albite NaAlSi3O8 C1 1

76.1.3.2 Oligoclase (Na,Ca)(Si,Al)4O8 C1 1

76.1.3.3 Andesine* (Na,Ca)(Si,Al)4O8 C1 1

76.1.3.4 Labradorite * (Ca,Na)(Si,Al)4O8 C1 1

76.1.3.5 Bytownite* (Ca,Na)(Si,Al)4O8 C1 1

76.1.3.6 Anorthite CaAl2Si2O8 P1,I1 1

Strunz Class:

VIII/J.07-50 VIII - Silicates

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

VIII/J.07 - Feldspar group, Anorthoclase - Anorthite - Banalcite series

VIII/J.07-10 Anorthoclase (Na,K)AlSi3O8 C1 1

VIII/J.07-20 Albite NaAlSi3O8 C1 1

VIII/J.07-30 Oligoclase (Na,Ca)(Si,Al)4O8 C1 1

VIII/J.07-40 Andesine* (Na,Ca)(Si,Al)4O8 C1 1

VIII/J.07-50 Labradorite (Ca,Na)(Si,Al)4O8 C1 1

VIII/J.07-60 Bytownite* (Ca,Na)(Si,Al)4O8 C1 1

VIII/J.07-70 Anorthite CaAl2Si2O8 P1,I1 1

VIII/J.07-75 Dmisteinbergite CaAl2Si2O8 P 6/mmm 6/m 2/m 2/m

VIII/J.07-80 Svyatoslavite CaAl2Si2O8 P 2₁ 2

VIII/J.07-90 Stronalsite SrNa2Al4Si4O16 I bam,Iba2 Ortho

VIII/J.07-100 Banalsite BaNa2Al4Si4O16 I bam 2/m 2/m 2/m

VIII/J.07-110 Filatovite! K[(Al,Zn)2(As,Si)2O8] I2/c 2/m

Other Labradorite Information

References:

NAME( Sinkankas66) PHYS. PROP.(Enc. of Minerals,2nd ed.,1990) OPTIC PROP.(Heinrich65)

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Labradorite

(Ca,Na)(Si,Al)4O8
Dana No: 76.1.3.4 Strunz No: VIII/J.07-50
Locality:

Notes: