cancrinite

{{Infobox mineral | name = Cancrinite | boxwidth = | boxbgcolor = | image = Cancrinite 3166.jpg | imagesize = | alt = | caption = Cancrinite | category = Tectosilicate minerals | group = Feldspathoid group, cancrinite group | formula = Na6Ca2[(CO3)2|Al6Si6O24]·2H2O | IMAsymbol = Ccn | strunz = 9.FB.05 | dana = | system = Hexagonal | class = Pyramidal (6) (same H-M symbol) | symmetry = P63 | unit cell = a = 12.67(9) Å, c = 5.15(4) Å; Z= 1 | color = Grey-green, white, yellow, blue, orange, reddish | habit = Rare as prismatic crystals; typically massive | twinning = Rare – lamellar | cleavage = Perfect on {100}, poor on {0001} | fracture = Irregular/uneven | tenacity = Brittle | mohs = 5–6 | luster = Vitreous, greasy, pearly | streak = White | diaphaneity = Transparent, translucent | gravity = 2.42 – 2.51 | density = | polish = | opticalprop = Uniaxial (+/−) | refractive = nω = 1.507 – 1.528 nε = 1.495 – 1.503 | birefringence = δ = 0.012 – 0.025 | pleochroism = | 2V = | dispersion = | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | fusibility = | diagnostic = | solubility = | impurities = | alteration = | other = | prop1 = | prop1text = | references = }}

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.