HEULANDITE (cabinet)

Heulandite refers to a series of tecto-silicate minerals within the zeolite group. Until 1997, it was classified as a distinct mineral species; however, the International Mineralogical Association redefined it as a series name that includes specific mineral species such as Heulandite-Ca, Heulandite-Na, Heulandite-K, Heulandite-Sr, and Heulandite-Ba, the latter being described in 2002. Heulandite-Ca, the most prevalent variant, is a hydrous calcium and aluminum silicate represented by the formula (Ca,Na)2−3Al3(Al,Si)2Si13O36·12H2O, with minor sodium and potassium often substituting for calcium. In the heulandite-Sr variety, strontium takes the place of calcium. The designation of species is based on the predominant element, although they are visually indistinguishable, and the term heulandite is still applied when specific testing has not been conducted.