Constituent
Name
Alunite
IMA name
Alunite
Class
non-silicate mineral
Compound type
sulfate
Constituent abundance in material
Relevance
main - minor
Arrangement
in multi-phases
Chemical composition
Formula
$KAl_3(SO_4)_2(OH)_6$
Chemical formula
KAl3(SO4)2(OH)6
Elemental formula
(K+) Al3 S2 O4 (O-)10 H6
Isotope mixture type
terrestrial abundance
  Formula Name Family Number min-max Isotope mole fraction State Relevance
$K^+$ Potassium(1+) cation element 1 constituent cation main
$Al$ Aluminium element 3 constituent element main
$(SO_4)^{2-}$ Sulfate anion chemical function 2 anionic radical main
$(OH)^-$ Hydroxide anion chemical function 6 anionic radical main
Chemical functions
  Function Number
$(SO_4)^{2-}$ 2
$(OH)^-$ 6
Chemical bonds
  Bond Number
$\dddot - \dddot - \dddot - S \dddot - O^{-1/2}$ 4
$O^--H$ 1
Oxides
Formula $K_{2}O$ $Al_{2}O_{3}$ $H_{2}O$ $SO_{3}$
Mass fraction (%) 11.37 36.92 13.05 38.66

Strunz

Class
sulfates - chromates - molybdates - tungstates (07)
Division
sulfates (selenates, etc.) with additional anions, without H2O (07.B)
Family
with medium-sized and large cations (07.BC)
Code
07.BC.10

Dana

Major class
sulfates, chromates, selenates (VI)
Class
anhydrous sulfates containing hydroxyl or halogen (30)
Type
where (A B)2 XO4 Zq (30.02)
Group
Alunite group (Alunite Subgroup) (30.02.04)
Code
30.02.04.01
Phase type
crystalline
Crystal system
trigonal
Crystal class
ditrigonal-pyramidal
Crystal class symbol
3m (C3v)
Crystal spacegroup
R3m
Molar mass
414.21 $g/mol$
Density
2.59 - 2.9 $g/cm^3$
Refringence type
uniaxial
Refringence sign
positive
Birefringence
0.020
Refraction index $n_{\alpha}$
1.572
Refraction index $n_{\beta}$
1.592
Color
white, gray, yellowish gray, reddish gray, yellowish white
Diaphaneity
transparent to translucent
Luster
vitreous