Constituent
Name
Anorthite
Class
silicate mineral
Compound type
tektosilicate
Comments
Anorthite: name by extension in the range Na=0-10%, K=0-10% of $(Ca,Na,K)Al_2Si_2O_8$
Relevance
main - major
Arrangement
heterogeneous in multi-phases
Mass fraction
18.77
Formula
$CaAl_2Si_2O_8$
Chemical formula
CaAl2Si2O8
Elemental formula
Ca Al2 Si2 O8
Isotope mixture type
terrestrial abundance
  Formula Name Family Number min-max Isotope mole fraction State Relevance
$Ca$ Calcium element 1 constituent element main
$Al$ Aluminium element 2 constituent element main
$Si$ Silicon element 2 constituent element main
$O$ Oxygen element 8 constituent element main
Composition comments
Typical formula: Na0.05Ca0.95Al1.95Si2.05O8 - Common replacements: Na, K (limited solid solution) - Common impurities: Ti, Fe
Oxides
Formula $CaO$ $Na_{2}O$ $K_{2}O$ $Al_{2}O_{3}$ $SiO_{2}$
Mass fraction (%) 19.76 35.84 44.4
Oxides comments
frequently also Na2O ~0.6% (CaO=19.2%)

Strunz

Class
silicates (09)
Division
tektosilicate without zeolitic H2O (09.F)
Family
Tektosilicates without additional non-tetrahedral anions, (Al,B):Si = 1:1 (09.FA)
Code
09.FA.35

Dana

Major class
silicates (VIII)
Class
tectosilicate Al-Si framework (76)
Type
with Al-Si frameworks (76.01)
Group
Plagioclase series (76.01.03)
Code
76.01.03.06
Phase type
crystalline
Crystal system
triclinic
Crystal class
pinacoidal
Crystal class symbol
-1 (Ci)
Crystal spacegroup
P-1
Texture
polycrystalline
Molar mass
277.41 $g/mol$
Density
2.72 - 2.75 $g/cm^3$
Refringence type
biaxial
Refringence sign
negative
Birefringence
0.0110 - 0.0120
Refraction index $n_{\alpha}$
1.572 - 1.576
Refraction index $n_{\beta}$
1.5785 - 1.5832
Refraction index $n_{\gamma}$
1.583 - 1.588
Dispersion V
relatively weak
Color
colorless, gray, white, red, reddish gray
Diaphaneity
transparent to translucent
Luster
vitreous