Carnallite (also carnalite) is an evaporite mineral, a hydrated potassium with formula KMgCl3·6(H2O). It is variably colored yellow to white, reddish, and sometimes colorless or blue. It is usually massive to fibrous with rare pseudohexagonal orthorhombic crystals. The mineral is deliquescent (absorbs moisture from the surrounding air) and specimens must be stored in an airtight container.
Carnallite occurs with a sequence of potassium and magnesium evaporite minerals: sylvite , polyhalite. Carnallite is an uncommon double chloride mineral that only forms under specific environmental conditions in an evaporating sea or sedimentary basin. It is mined for both potassium and magnesium and occurs in the evaporite deposits of Carlsbad, New Mexico; the Paradox Basin ; Stassfurt, Russia in Saskatchewan, Canada through the Permian and Jordan by using evaporation pans to further concentrate the brine until carnallite precipitates, dredging the carnallite from the pans, and processing to remove the magnesium chloride from the potassium chloride
Carnallite was first described in 1856 from its type location of Stassfurt Deposit, Saxony-Anhalt. It was named for the Prussian Rudolf von Carnall