Mineral phase
IMA name
Hexahydrite
IMA Code
Hhy
Type
Class
non-silicate mineral
Compound type
sulfate
Chemical composition
Formula
$MgSO_4 \bullet 6H_2O$
Chemical formula
MgSO4•6H2O
Elemental formula
(Mg2+) S O8 (O-)2 H12
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 6 hydration main
Chemical functions
  Function Number
$(SO_4)^{2-}$ 1
$R-OH$ 2
Chemical bonds
  Bond Number
$\cdot Mg^{2+} \cdot O^{-}-$ 2
$-O \dots H-$ 12
$-O-H$ 2
$\dddot - \dddot - \dddot - S \dddot - O^{-1/2}$ 4
Oxides
Formula $MgO$ $SO_{3}$ $H_{2}O$
Mass fraction (%) 17.64 35.05 47.31

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.25

Dana

Major class
sulfates, chromates, selenates (VI)
Class
hydrated acid and sulfates (29)
Type
where AXO4.x(H2O) (29.06)
Group
Hexahydrite group (Hexahydrates, monoclinic: C2/c) (29.06.08)
Code
29.06.08.01
Phase type
crystalline
Crystal system
monoclinic
Crystal class
prismatic
Crystal class symbol
2/m (C2h)
Crystal spacegroup
C2/c
Molar mass
228.46 $g/mol$
Density
1.76 $g/cm^3$
State NTP
solid
Phase transitions
Phase transition type Other phases Temperature - Pressure
solid-solid Kieserite below 42% RH
solid-solid Epsomite above 51% RH
Phase transitions comments
hydrates to Epsomite in humid air
Refringence type
biaxial
Refringence sign
negative
Birefringence
0.030
Refraction index $n_{\alpha}$
1.426
Refraction index $n_{\beta}$
1.453
Refraction index $n_{\gamma}$
1.456
Pure color
colorless
Color
colorless, white, greenish
Diaphaneity
transparent to opaque
Luster
vitreous
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