Antarcticite

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Antarcticite
General
Category Halide mineral
Formula
(repeating unit)
CaCl2·6H2O
Strunz classification 3.BB.30
Crystal system Trigonal
Crystal class Trapezohedral (32)
H-M symbol: (32)
Space group P321
Unit cell a = 7.9, c = 3.95 [Å]; Z = 1
Identification
Color Colorless
Crystal habit Occurs as groups of acicular crystals
Cleavage Perfect on {0001}, very good on {1010}
Tenacity Brittle
Mohs scale hardness 2 - 3
Luster Vitreous
Diaphaneity Transparent
Specific gravity 1.715
Optical properties Uniaxial (-)
Refractive index nω = 1.550 nε = 1.490 - 1.500
Birefringence δ = 0.060
Other characteristics Deliquescent
References [1][2][3]

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]

References[edit]