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Cancrinite 3166.jpg
Category Feldspathoid
(repeating unit)
Strunz classification 9.FB.05
Crystal system Hexagonal
Crystal class Pyramidal (6)
(same H-M symbol)
Space group P63
Unit cell a = 12.67(9) Å,
c = 5.15(4) Å; Z= 1
Color Grey-green, white, yellow, blue, orange, reddish
Crystal habit Rare as prismatic crystals; typically massive
Twinning Rare - lamellar
Cleavage Perfect on {1010}, poor on {0001}
Fracture Irregular/uneven
Tenacity Brittle
Mohs scale hardness 5-6
Luster Vitreous, greasy, pearly
Streak White
Diaphaneity Transparent, translucent
Specific gravity 2.42 - 2.51
Optical properties Uniaxial (+/-)
Refractive index nω = 1.507 - 1.528 nε = 1.495 - 1.503
Birefringence δ = 0.012 - 0.025
References [1][2][3]

Cancrinite is a complex carbonate and silicate of sodium, calcium and aluminium with the formula Na6Ca2[(CO3)2|Al6Si6O24]·2H2O. It is classed as a member of the feldspathoid group of minerals; the alkali feldspars that are poor in silica. Yellow, orange, pink, white or even blue, it has a vitreous or pearly luster; a hardness of 5-6 and an uneven conchoidal fracture. It is unusual among the silicate minerals in that it will effervesce with hydrochloric acid due to the associated carbonate ions.

Found originally in 1839 in the Ural Mountains, it is named after Georg von Cancrin, a Russian minister of finance.[1]