Mineral phase
IMA name
Starkeyite
Secondary names
Leonhardtite
IMA Code
Ske
Type
Class
non-silicate mineral
Compound type
sulfate
Chemical composition
Formula
$MgSO_4 \bullet 4H_2O$
Chemical formula
MgSO4•4H2O
Elemental formula
(Mg2+) S O6 (O-)2 H8
Isotope mixture type
terrestrial abundance
  Formula Name Family Number min-max Isotope mole fraction State Relevance
$Mg^{2+}$ Magnesium(II) cation element 1 constituent cation main
$(SO_4)^{2-}$ Sulfate anion chemical function 1 anionic radical main
$H_2O$ Water molecule 4 hydration main
Composition comments
Soluble in water. Common impurities: Fe
Chemical functions
  Function Number
$(SO_4)^{2-}$ 1
$R-OH$ 2
Chemical bonds
  Bond Number
$\cdot Mg^{2+} \cdot O^{-}-$ 2
$-O \dots H-$ 8
$-O-H$ 2
$\dddot - \dddot - \dddot - S \dddot - O^{-1/2}$ 4
Oxides
Formula $MgO$ $SO_{3}$ $H_{2}O$
Mass fraction (%) 20.94 41.61 37.45

Strunz

Class
sulfates - chromates - molybdates - tungstates (07)
Division
sulfates (selenates, etc.) without additional anions, with H2O (07.C)
Family
with only medium-sized cations (07.CB)
Code
07.CB.15

Dana

Major class
sulfates, chromates, selenates (VI)
Class
hydrated acid and sulfates (29)
Type
where AXO4.x(H2O) (29.06)
Group
Rozenite group (Tetrahydrates, monoclinic) (29.06.06)
Code
29.06.06.02
Phase type
crystalline
Crystal system
monoclinic
Crystal class
prismatic
Crystal class symbol
2/m (C2h)
Crystal spacegroup
P2(1)/m
Molar mass
192.43 $g/mol$
Density
2.01 $g/cm^3$
State NTP
solid
Refringence type
biaxial
Refringence sign
positive
Birefringence
0.007
Refraction index $n_{\alpha}$
1.49
Refraction index $n_{\beta}$
1.491
Refraction index $n_{\gamma}$
1.497
Dispersion V
none
Pure color
colorless
Color
colorless, white, yellowish, greenish
Diaphaneity
transparent to opaque
Luster
earthy
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