CARNALLITE

    Class : Halides
    Subclass : Chlorides
    Crystal system : Orthorhombic
    Chemistry : KMgCl3 6H2O
    Rarity : Quite common

Carnallite is an important potassium ore, typical of evaporitic deposits. In these deposits, carnallite is one of the last chlorides to precipitate from the final brines enriched in magnesium and potassium, well after the deposition of halite, kieserite and sylvite. Highly hydroscopic, a humid atmosphere causes it to “melt” very easily into a thick brine. It owes its name to the German mining engineer Rudolph von Carnall. It is a mineral which generally occurs in beds or in shapeless granular masses, exceptionally in pseudohexagonal or thick tabular pyramidal crystals. It is colorless, milky white, sometimes colored red by oriented hematite inclusions.

Main photo : Carnallite from Kerr McGee, New Mexico, USA © Chris Stefano

Carnallite in the World

Carnallite is the main mineral of the large potash deposits in Germany (Stassfurt region), deposited during the retreat of the Zechstein Sea at the end of the Permian, approximately 235 million years ago. Beautiful crystals come from this district (Beienrode, near Brunswick). It is also a frequent mineral in the salt lakes of the United States, Ethiopia (Dalol), and in the salt layers of Poland.

Carnallite in France

In France, carnallite is common in the Mulhouse basin (Alsace).

Twinning

No twin known for this mineral species.

Fakes and treatments

No fake identified for this mineral species.


Hardness : 2.5
Density : 1.602
Fracture : Conchoidal
Streak : White

TP : Translucent to transparent
RI : 1.465 to 1.496
Birefringence : 0.029 to 0.030
Optical character : Biaxial +
Pleochroism : None
Fluorescence : None

Solubility : Water


Magnetism : None
Radioactivity : None