HEXAHYDRITE

    Class : Sulfates, chromates, molybdates
    Subclass : Hydrated sulfates
    Crystal system : Monoclinic
    Chemistry : MgSO4 6H2O
    Rarity : Uncommon

Hexahydrite is a secondary hydrated magnesium sulfate formed by partial dehydration of epsomite (loss of a water molecule), a primary mineral of evaporitic deposits or secondary of hydrothermal deposits and then formed by alteration of sulfides. Hexahydrite very frequently accompanies epsomite, which it covers with efflorescence or pseudomorph. Its name comes from the Greek hexa (six) and hudor (water) because it contains 6 water molecules per structural formula. Hexahydrite is rarely thick tabular crystals and usually occurs as efflorescences or fibrous, colorless, white or pale greenish columnar masses.

Main photo : Hexahydrite from Zastávka, Czech Republic © Zbynek Burival - White parts are dehydrated

Hexahydrite in the World

Hexahydrite is known in beautiful efflorescences on epsomite in Oroville (Washington), and epsomite pseudomorphs in Klano and Kelcany (Czech Republic). Other occurrences of this mineral include the Saki salt lakes in Crimea (Ukraine) where hexahydrite accompanies halite.

Hexahydrite in France

In France, hexahydrite is reported at Lubilhac near Brioude (Haute-Loire) as well as at Avion near Lens (Pas-de-Calais).

Twinning

Twins are known on {001} and on {110}.

Fakes and treatments

No fakes recorded for this mineral species.


Hardness : 2 to 2.5
Density : 1.757
Fracture : Conchoidal
Streak : White

TP : Translucent to transparent
RI : 1.426 to 1.456
Birefringence : 0.030
Optical character : Biaxial -
Pleochroism : None
Fluorescence : None

Solubility : Water

Magnetism : NoneRadioactivity : None