NaCa2Al5Si13O36 14H2O, Hydrated sodium calcium aluminum silicate
At one time heulandite and stilbite were considered to be identical minerals.  After they were found to be two separate species, in 1818, the name desmine ("a bundle") was proposed for stilbite, and this name is still employed in Germany.  The English name "stilbite" is from the Greek stilbein = to shine, because of the pearly luster of the {010} faces.
Stilbite is a common and perhaps the most popular zeolite mineral for collectors.  Stilbite crystals can aggregate to form a structure resembling wheat sheaves.  This hourglass structure looks like several crystals stacked parallel to each other with the tops and bottoms of this structure fanning out while the middle remains thin.  Stilbite's hallmark crystal habit is unique to stilbite and a rarer but related zeolite called stellerite.  Whether in the wheat sheaves or not, stilbite can be a handsome specimen with its pearly luster and often colorful pink tints.  Stilbite commonly forms nice crystals inside the petrified bubbles (called vesicles) of volcanic rocks that have undergone a small amount of metamorphism.
Stilbite's structure has a typical zeolite openness about it that allows large ions and molecules to reside and actually move around inside the overall framework.  The structure contains open channels that allow water and large ions to travel into and out of the crystal structure.  The size of these channels controls the size of the molecules or ions and therefore a zeolite like stilbite can act as a chemical sieve.  Stilbite's structure contains rings of alumino-silicate tetrahedra oriented in one direction and this produces the prominent pinacoid faces, the perfect cleavage and the unique luster on those faces.
Stilbite occurs in the basalt formation in the Goboboseb area at Brandberg and also in the Grootberg area, and from the Erongo mountains in Namibia.  Only a handful of very good specimens make it to the market and their way to collectors.  Stilbite occurs in the Goboboseb basalt with quartz and also with heulandite and bladed barite.
        Stilbite with Epidote, Erongo                                   Stilbite from Grootberg
Stilbite occurs with epidote and orthoclase in the Erongo district near the Spitskoppe.  Well-formedsprays of stilbite with orthoclase and deep green sprays of epidote were found.
All specimen photos from the Pieter de Bruyn Collection
Pieter de Bruyn, KM Minerals, Kuruman.
References: Wikipedia,