Mineral phase
IMA name
Feldspars group
Type
Class
silicate mineral
Compound type
tektosilicate
Comments
K-Na series of Feldspar
Compositional phase diagram of the different minerals of the feldspar solid solution (Wikipedia - By Muskid - Own work, CC BY-SA 4.0)
Chemical composition
Formula
$(K,Na,Ca,Ba)(Al,Si)AlSi_2O_8$
Chemical formula
(Ca,Na,K,Ba)(Al,Si)AlSi2O8
Elemental formula
(Ca)0-1 (Na)0-1 (K)0-1 (Ba)0-1 (Al)1-2 (Si)2-3 O8
Isotope mixture type
terrestrial abundance
  Formula Name Family Number min-max Isotope mole fraction State Relevance
$Ca$ Calcium element 0 - 1 constituent element main
$Na$ Sodium element 0 - 1 constituent element main
$K$ Potassium element 0 - 1 constituent element main
$Ba$ Barium element 0 - 1 constituent element main
$Al$ Aluminium element 1 - 2 constituent element main
$Si$ Silicon element 2 - 3 constituent element main
$O$ Oxygen element 8 constituent element main
Composition comments
Limited solid solution beetween Ca-K - Common impurities: Mg, Fe, Rb
Oxides
Formula $CaO$ $Na_{2}O$ $K_{2}O$ $BaO$ $Al_{2}O_{3}$ $SiO_{2}$
Mass fraction (%)

Strunz

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

Dana

Major class
silicates (VIII)
Class
tectosilicate Al-Si framework (76)
Type
with Al-Si frameworks (76.01)
Group
N/A (N/A)
End-members
Members
  • Orthoclase (Na (Ab) = 0-10% - Ca = 0-10% - K (Or) = 90-100% (monoclinic))
  • Microcline (Na (Ab) = 0-10% - Ca = 0-10% - K (Or) = 90-100% (triclinic))
  • Sanidine (Na (Ab) = 10-64% - Ca = 0-10% - K (Or) = 36-90% (monoclinic))
  • Anorthoclase (Na (Ab) = 64-90% - Ca = 0-10% - K (Or) = 10-36% (triclinic))
  • Albite (Na (Ab) = 90-100% - Ca = 0-10% - K (Or) = 0-10% (triclinic))
  • Oligoclase (Na (Ab) = 70-90% - Ca = 10-30% - K (Or) = 0-10% (triclinic))
  • Andesine (Na (Ab) = 50-70% - Ca = 30-50% - K (Or) = 0-10% (triclinic))
  • Labradorite (Na (Ab) = 30-50% - Ca = 50-70% - K (Or) = 0-10% (triclinic))
  • Bytownite (Na (Ab) = 10-30% - Ca = 80-90% - K (Or) = 0-10% (triclinic))
  • Anorthite (Na (Ab) = 0-10% - Ca (An) = 90-100% - K (Or) = 0-10% (triclinic))
Phase type
crystalline
Crystal system
various
Crystal class
various
Crystal class symbol
various
Crystal spacegroup
various
Molar mass
263.02 - 278.33 $g/mol$
Density
2.56 - 2.76 $g/cm^3$
State NTP
solid
Refringence type
biaxial
Refringence sign
positive or negative
Birefringence
0.005 - 0.012
Refraction index $n_{\alpha}$
1.518 - 1.576
Refraction index $n_{\beta}$
1.522 - 1.583
Refraction index $n_{\gamma}$
1.523 - 1.588
Dispersion V
weak to relatively strong
Color
colorless, white, gray, greenish, bluish green, grayish yellow, white, pink
Diaphaneity
transparent to subtranslucent
Luster
vitreous
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