Heulandite-K
Heulandite is the name of a series of tectosilicate minerals of the zeolite group. Prior to 1997, heulandite was recognized as a mineral species, but a reclassification in 1997 by the International Mineralogical Association changed it to a series name, with the mineral species being named: Heulandite-Ca Heulandite-Na Heulandite-K Heulandite-Sr Heulandite-Ba (described in 2002). Heulandite-Ca, the most common of these, is a hydrous calcium and aluminium silicate with the formula (Ca,Na)5(Si27Al9)O72·26H2O. Small amounts of sodium and potassium are usually present replacing part of the calcium.
Intro adapted from Wikipedia (CC BY-SA).
Heulandite-K is an IMA-recognized mineral species in the silicate class, with the chemical formula (K,Ca,Na)₅(Si₂₇Al₉)O₇₂·26H₂O.
It is a member of the Heulandite structural group.
IMA symbol Hul-K, IMA status: approved, named in 1997.