Cancrinite

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Cancrinite
Cancrinite 3166.jpg
Cancrinite
General
CategoryFeldspathoid
Formula
(repeating unit)
Na6Ca2[(CO3)2|Al6Si6O24]·2H2O
Strunz classification9.FB.05
Crystal systemHexagonal
Crystal classPyramidal (6)
(same H-M symbol)
Space groupP63
Unit cella = 12.67(9) Å,
c = 5.15(4) Å; Z= 1
Identification
ColorGrey-green, white, yellow, blue, orange, reddish
Crystal habitRare as prismatic crystals; typically massive
TwinningRare – lamellar
CleavagePerfect on {1010}, poor on {0001}
FractureIrregular/uneven
TenacityBrittle
Mohs scale hardness5–6
LusterVitreous, greasy, pearly
StreakWhite
DiaphaneityTransparent, translucent
Specific gravity2.42 – 2.51
Optical propertiesUniaxial (+/-)
Refractive indexnω = 1.507 – 1.528 nε = 1.495 – 1.503
Birefringenceδ = 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]

References[edit]