Stilbite

Stilbite is a hydrous calcium sodium aluminosilicate belonging to the zeolite group, forming a series between stilbite-Ca and the rarer sodium-dominant stilbite-Na. Named from the Greek for "to glitter," in reference to its pearly, vitreous luster, stilbite is instantly recognizable for its distinctive sheaf-like or bow-tie aggregates of flattened, tabular monoclinic crystals, often described as pseudo-orthorhombic. Colors range from pure white and cream to salmon-pink, orange, brown and brick-red, with the salmon-pink hue being especially prized by collectors. It typically forms in the amygdaloidal cavities of basaltic volcanic rock alongside other zeolites such as heulandite, apophyllite, laumontite, and with prehnite, calcite and quartz.

The most prolific source of fine stilbite in the world is the Deccan Traps of western India, where the tholeiitic basalt plateaux near Nasik and Pune (including the classic Poona district) yield abundant salmon-pink sheaf-like crystals often intergrown with pale green apophyllite, decreasing in abundance toward the coast near Mumbai. Reddish-orange stilbite-Ca specimens are also well known from the Jalgaon District of Maharashtra. Iceland is considered the type locality for stilbite-Ca, with the Helgusta Iceland Spar Mine along Reydarfjordur and the classic locality of Berufjord near Djupivogur producing excellent white bow ties on calcite and quartz. The type locality for stilbite-Na is Cape Pula in Sardinia, Italy, where lustrous white to pink blades occur in weathered volcanic andesite. Other historically important localities include the Faroe Islands, the Isle of Skye in Scotland, Old Kilpatrick near Glasgow with its brick-red crystals, the Bay of Fundy in Nova Scotia (where stilbite is the provincial mineral), brown sheaf-like groups from Paterson, New Jersey, and occurrences in North Carolina and at Grua in Norway.

For mineral collectors, stilbite is treasured for the aesthetic appeal of its radiating sheaf and bow-tie habits, its warm color range, and its close association with other classic zeolite-group species that make Deccan Trap and Icelandic vugs so collectible. Prior to a 1997 IMA reclassification stilbite was treated as a single species; today specimens are more precisely labeled stilbite-Ca or stilbite-Na based on chemical analysis, though the two are visually indistinguishable in hand specimen. Combined with its frequent pairing with cavansite, apophyllite, heulandite and calcite, stilbite remains one of the most sought-after zeolites for systematic and aesthetic mineral collections alike.