Constituent
- Name
- plagioclase
- IMA name
- Albite-Anorthite series
- Class
- silicate mineral
- Compound type
- tektosilicate
- Comments
- Plagioclase is a wider series $(Na,Ca)(Si,Al)_4O_8$ of the feldspar group
- Relevance
- main - major
- Arrangement
- heterogeneous in multi-phases
- Abundance comments
- modal abundance computed by Mandon et al. 2021: ~ 0.75 vol%
- Formula
- $(Na,Ca)(Al,Si)AlSi_2O_8$
- Chemical formula
- ((Na)x(Ca)1-x)((Al)1-x(Si)x)AlSi2O8
- Elemental formula
- (Na)0-1 (Ca)0-1 (Al)1-2 (Si)2-3 O8
- Isotope mixture type
- terrestrial abundance
- Composition comments
- Common replacement: K (limited solid solution) - Common impurities: Ti, Fe, Mg, H2O
- Oxides
-
Formula $Na_{2}O$ $CaO$ $K_{2}O$ $Al_{2}O_{3}$ $SiO_{2}$ Mass fraction (%)
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)
- Phase type
- crystalline
- Crystal system
- triclinic
- Crystal class
- pinacoidal
- Crystal class symbol
- -1 (Ci)
- Crystal spacegroup
- P-1
- Molar mass
- 263.02 - 277.41 $g/mol$
- Density
- 2.61 - 2.76 $g/cm^3$
- Refringence type
- biaxial
- Refringence sign
- positive or negative
- Birefringence
- 0.009 - 0.012
- Refraction index $n_{\alpha}$
- 1.528 - 1.576
- Refraction index $n_{\beta}$
- 1.532 - 1.583
- Refraction index $n_{\gamma}$
- 1.538 - 1.588
- Dispersion V
- weak to relatively weak
- Color
- white, gray, bluish white, reddish white, greenish white
- Diaphaneity
- transparent to subtranslucent
- Luster
- vitreous