What is "heulandite"

Heulandite \Heu"land*ite\, n. [After Heuland, an English mineralogist.] (Min.) A mineral of the Zeolite family, often occurring in amygdaloid, in foliated masses, and also in monoclinic crystals with pearly luster on the cleavage face. It is a hydrous silicate of alumina and lime.

n. (context mineral English) A common mineral of the zeolite group with monoclinic crystals, the most usual form being heulandite-Ca (calcium,sodium)_2-3aluminum₃(Al,silicon)₂Si₁₃oxygen₃₆·12water.

n. a group of minerals of the zeolite family consisting of a hydrous aluminum silicate of sodium and calcium

Heulandite is the name of a series of tecto-silicate 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, (Ca,Na)Al(Al,Si)SiO·12HO. Small amounts of sodium and potassium are usually present replacing part of the calcium. Strontium replaces calcium in the heulandite-Sr variety. The appropriate species name depends on the dominant element. The species are visually indistinguishable, and the series name heulandite is still used whenever testing has not been performed.