POLYHALITE

    Class : Sulfates, chromates, molybdates
    Subclass : Sulfates
    Crystal system : Triclinic
    Chemistry : K2Ca2Mg(SO4)4 2H2O
    Rarity : Common

Polyhalite is a multiple sulfate of marine evaporitic formations, sometimes encountered in volcanic fumaroles. Its name comes from the Greek polus (many) and hals (salts) in allusion to its chemical composition. Polyhalite is usually massive and fibrous, rarely in small tabular or elongated crystals (up to 10 cm). Its color is normally colorless to white but polyhalite is frequently colored brick red, flesh pink or dark beige by inclusions of iron oxides. It is a mineral associated with other classic salts of these evaporites (halite, sylvite, carnallite, kieserite, etc...). It is a potassium ore.

Main photo : 10 cm polyhalite from salt mine of Hallstatt, Austria © Gerhard Brandstetter

Polyhalite in the World

Polyhalite is common in evaporitic deposits, including those in Germany (Stassfurt), Austria (Bad Ischl, Hallstatt), Kazakhstan and New Mexico. Among the deposits of volcanic fumaroles, the most remarkable is that of Vesuvius (Italy).

Polyhalite in France

In France polyhalite is known in Varangéville (Meurthe-et-Moselle) and St-Pandelon (Landes).

Twinning

Twins on {010} and {100} are very common and often polysynthetic.

Fakes and treatments

No fakes listed for this mineral species.


Hardness : 2.5 to 3.5
Density : 2.78
Fracture : Undetermined
Streak : White to reddish

TP : Translucent to transparent
RI : 1.546 to 1.567
Birefringence : 0.021
Optical character : Biaxial -
Pleochroism : None
Fluorescence : None

Solubility : Water

Magnetism : NoneRadioactivity : None