Mineral phase
- IMA name
- Anorthite
- Secondary names
- Indianite
- Class
- silicate mineral
- Compound type
- tektosilicate
- Comments
- Anorthite: name by extension in the range Na=0-10%, K=0-10% of $(Ca,Na,K)Al_2Si_2O_8$
- Formula
- $CaAl_2Si_2O_8$
- Chemical formula
- CaAl2Si2O8
- Elemental formula
- Ca Al2 Si2 O8
- Isotope mixture type
- terrestrial abundance
- 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
- 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
- Molar mass
- 277.41 $g/mol$
- Density
- 2.72 - 2.75 $g/cm^3$
- State NTP
- solid
- 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
- Pure color
- colorless
- Color
- colorless, gray, white, red, reddish gray
- Diaphaneity
- transparent to translucent
- Luster
- vitreous