Anorthite Mineral Data

General Anorthite Information

Chemical Formula:

CaAl2Si2O8

Composition:

Molecular Weight = 277.41 gm

Sodium 0.41 % Na 0.56 % Na₂O

Calcium 13.72 % Ca 19.20 % CaO

Aluminum 18.97 % Al 35.84 % Al₂O₃

Silicon 20.75 % Si 44.40 % SiO₂

Oxygen 46.14 % O

______ ______

100.00 % 100.00 % = TOTAL OXIDE

Empirical Formula:

Na_0.05Ca_0.95Al_1.95Si_2.05O₈

Environment:

Magmatic and metamorphic rocks.

IMA Status:

Valid Species (Pre-IMA) 1823

Locality:

Monte Somma and Valle di Fassa, Italy. Link to MinDat.org Location Data.

Name Origin:

From the Greek, an + orthos, "not upright" in allusion to the oblique crystals.

Name Pronunciation:

Anorthite + Pronunciation

Synonym:

Ab0

An100

ICSD 654

Indianite

PDF 41-1486

Anorthite Image

Images:

Anorthite Plagioclase

Comments: Opaque white crystal of anorthite with dark brown solidified lava coating.
Location: Miyake-jima, Shizuoka, Japan. Scale: See Photo.
© Jeff Weissman / Photographic Guide to Mineral Species

Anorthite Crystallography

Axial Ratios:

a:b:c =0.635:1:1.1003

Cell Dimensions:

a = 8.177, b = 12.877, c = 14.169, Z = 8; alpha = 93.166°, beta = 115.85°, gamma = 91.216° V = 1,340.29 Den(Calc)= 2.75

Crystal System:

Triclinic - Pinacoidal H-M Symbol ( 1) Space Group: P1,I1

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

By Intensity(I/I_o): 3.2(1), 3.18(0.75), 4.04(0.6),

Forms:

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Forms: ( 0 0 1) ( 1 0 0) ( 1 0 1) ( 0 1 0)

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Physical Properties of Anorthite

Cleavage:

{001} Perfect, {010} Good

Color:

Colorless, Gray, White, Red, Reddish gray.

Density:

2.72 - 2.75, Average = 2.73

Diaphaneity:

Transparent to Subtransparent to translucent

Fracture:

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

Habit:

Euhedral Crystals - Occurs as well-formed crystals showing good external form.

Habit:

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

Habit:

Striated - Parallel lines on crystal surface or cleavage face.

Hardness:

6 - Orthoclase

Luminescence:

Non-fluorescent.

Luster:

Vitreous (Glassy)

Streak:

white

Optical Properties of Anorthite

Gladstone-Dale:

CI meas= -0.02 (Excellent) - where the CI = (1-KPDmeas/KC)
CI calc= -0.015 (Superior) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.211,KPDmeas= 0.2121,KC= 0.2079
Ncalc = 1.57

Optical Data:

Biaxial (-), a=1.572-1.576, b=1.5785-1.5832, g=1.583-1.588, bire=0.0110-0.0120, 2V(Calc)=78, 2V(Meas)=78. Dispersion relatively weak.

Pleochroism (x):

colorless.

Pleochroism (y):

colorless.

Calculated Properties of Anorthite

Electron Density:

Bulk Density (Electron Density)=2.73 gm/cc
note: Specific Gravity of Anorthite =2.75 gm/cc.

Fermion Index:

Fermion Index = 0.01
Boson Index = 0.99

Photoelectric:

PE_Anorthite= 3.05 barns/electron
U=PE_Anorthite x rElectron Density= 8.32 barns/cc.

Radioactivity:

GRapi = 0 (Gamma Ray American Petroleum Institute Units)
Anorthite is Not Radioactive

Anorthite Classification

Dana Class:

76.01.03.06 (76)Tectosilicate Al-Si Framework

(76.01)with Al-Si frameworks

(76.01.03)Plagioclase series

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

76.01.03.01 Albite NaAlSi3O8 C1 1

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

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

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

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

76.01.03.06 Anorthite CaAl2Si2O8 P1,I1 1

Strunz Class:

09.FA.35 09 - SILICATES (Germanates)

09.F - Tektosilicates without Zeolitic H2O

09.FA -Tektosilicates without additional non-tetrahedral anions, (Al,B):Si = 1:1

09.FA.35 Albite NaAlSi3O8 C1 1

09.FA.35 Bytownite* (Ca,Na)(Si,Al)4O8 C1 1

09.FA.35 Anorthite CaAl2Si2O8 P1,I1 1

09.FA.35 Andesine* (Na,Ca)(Si,Al)4O8 C1 1

09.FA.35 Labradorite* (Ca,Na)(Si,Al)4O8 C1 1

09.FA.35 Oligoclase (Na,Ca)(Si,Al)4O8 C1 1

09.FA.35 Reedmergnerite NaBSi3O8 C1 1

09.FA.35 Plagioclase* (Na,Ca)(Si,Al)4O8 C1 1

Other Anorthite Information

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Anorthite

CaAl2Si2O8
Dana No: 76.01.03.06 Strunz No: 09.FA.35
Locality:

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