Mineral phase
IMA name
Orthoclase
Secondary names
Orthose
CAS number
12251-44-4
Type
Class
silicate mineral
Compound type
tektosilicate
Comments
Dimorphous with Microcline
Chemical composition
Formula
$KAlSi_3O_8$
Chemical formula
KAlSi3O8
Elemental formula
K Al Si3 O8
Isotope mixture type
terrestrial abundance
  Formula Name Family Number min-max Isotope mole fraction State Relevance
$K$ Potassium element 1 constituent element main
$Al$ Aluminium element 1 constituent element main
$Si$ Silicon element 3 constituent element main
$O$ Oxygen element 8 constituent element main
Composition comments
Common replacements: Na, Ba, Ca - Common impurities: Fe, Rb
Oxides
Formula $K_{2}O$ $Na_{2}O$ $BaO$ $CaO$ $Al_{2}O_{3}$ $SiO_{2}$
Mass fraction (%) 16.92 18.32 64.76

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.30

Dana

Major class
silicates (VIII)
Class
tectosilicate Al-Si framework (76)
Type
with Al-Si frameworks (76.01)
Group
K (Na,Ba) feldspars (76.01.01)
Code
76.01.01.01
Phase type
crystalline
Crystal system
monoclinic
Crystal class
prismatic
Crystal class symbol
2/m (C2h)
Crystal spacegroup
C2/m
Molar mass
278.33 $g/mol$
Density
2.56 $g/cm^3$
State NTP
solid
Refringence type
biaxial
Refringence sign
negative
Birefringence
0.0050 - 0.0060
Refraction index $n_{\alpha}$
1.518
Refraction index $n_{\beta}$
1.522
Refraction index $n_{\gamma}$
1.523 - 1.524
Dispersion V
relatively strong
Pure color
colorless
Color
colorless, greenish, grayish yellow, white, pink
Diaphaneity
transparent to translucent
Luster
vitreous
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