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CategoryHalide mineral
(repeating unit)
Strunz classification3.BB.30
Crystal systemTrigonal
Crystal classTrapezohedral (32)
H-M symbol: (32)
Space groupP321
Unit cella = 7.9, c = 3.95 [Å]; Z = 1
Crystal habitOccurs as groups of acicular crystals
CleavagePerfect on {0001}, very good on {1010}
Mohs scale hardness2 - 3
Specific gravity1.715
Optical propertiesUniaxial (-)
Refractive indexnω = 1.550 nε = 1.490 - 1.500
Birefringenceδ = 0.060
Other characteristicsDeliquescent

Antarcticite is an uncommon calcium chloride hexahydrate mineral with formula: CaCl2·6H2O. It forms colorless acicular trigonal crystals. It is hygroscopic and has a low specific gravity of 1.715.

As its name implies, it was first described in 1965 for an occurrence in Antarctica where it occurs as crystalline precipitate from a highly saline brine in Don Juan Pond, in the west end of Wright Valley, Victoria Land. This discovery was made by Japanese geochemists Tetsuya Torii and Joyo Ossaka.[4] It was also reported from brine in Bristol Dry Lake, California, and stratified brine within blue holes on North Andros Island in the Bahamas. It has also been noted within fluid inclusions within quartz in pegmatite bodies in the Bushveld complex of South Africa. It occurs in association with halite, gypsum and celestine in the California dry lake.[1]

A similar mineral, sinjarite, the dihydrate of calcium chloride, crystallizes in the tetragonal system.[5] Hydrophilite is a now discredited calcium chloride mineral that is considered to be either antarcticite or sinjarite.[6]