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.