Cancrinite

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.

Cancrinite
Cancrinite
General
Category	Tectosilicate minerals, feldspathoid group, cancrinite group
Formula	Na6Ca2[(CO3)2|Al6Si6O24]·2H2O
IMA symbol	Ccn[1]
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
Identification
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	[2][3][4]

Found originally in 1839 in the Ural Mountains, it is named after Georg von Cancrin, a Russian minister of finance.^[2]