Mineral phase
- IMA name
- Alkali feldspars
- Secondary names
- Potassium feldspars, K-feldspars
- Class
- silicate mineral
- Compound type
- tektosilicate
- Comments
- K-Na series of Feldspar
- Formula
- $(K,Na,Ca)(Al,Si)_4O_8$ - Ca < 0.1-0.3
- Chemical formula
- (K,Na,Ca)(Al,Si)4O8
- Elemental formula
- (K)0-1 (Na)0-1 (Ca)0-0.3 Al Si3 O8
- Isotope mixture type
- terrestrial abundance
- Composition comments
- Ca has limited solid solution - Common replacements: Ba - Common impurities: Mg, Fe, Rb, H2O
- Oxides
-
Formula $K_{2}O$ $Na_{2}O$ $CaO$ $Al_{2}O_{3}$ $SiO_{2}$ 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.30
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))
- 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 - 2.63 $g/cm^3$
- State NTP
- solid
- Refringence type
- biaxial
- Refringence sign
- positive or negative
- Birefringence
- 0.005 - 0.010
- Refraction index $n_{\alpha}$
- 1.518 - 1.533
- Refraction index $n_{\beta}$
- 1.522 - 1.537
- Refraction index $n_{\gamma}$
- 1.523 - 1.542
- Dispersion V
- weak to relatively strong
- Color
- colorless, white, gray, greenish, bluish green, grayish yellow, white, pink
- Diaphaneity
- transparent to subtranslucent
- Luster
- vitreous