wairakite

wairakite, hydrated calcium aluminosilicate mineral present in hot-spring deposits, notably those at Wairakei, New Zealand, and Onikobe, Japan. Like analcite, wairakite has been assigned to two mineral families: it is regarded as a feldspathoid because of its chemical properties, molecular structure, and mode of formation but as a zeolite because of its ion-exchange and reversible dehydration behaviour. Wairakite forms colourless, often twinned crystals of monoclinic symmetry; its chemical formula is CaAl₂Si₄O₁₂ · 2H₂O. Several other zeolite minerals are converted to wairakite in the presence of water at high temperatures and pressures.