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Download hereGENERAL DESCRIPTION
Epistilbite is an hydrated calcium aluminosilicate that belongs to the group of zeolites. It is typical of basaltic vacuoles as it is formed by weathering of the hosting basalts, which were also affected by a weak metamorphism. One also finds it in some pegmatites.
Its name points out that of the stilbite with which it can be confused. Nevertheless, stilbite forms broad clusters of cristals that epistilbite only forms very seldomly. One finds it as flattened crystals. It is often colourless, sometimes reddish white but also pinky.
Beautiful crystals come from Iceland (Berufjord), in the island of Skye (Scotland), in the Hawaiian basalts, the pegmatite quarry of Bedford (New York) and Nasik/Poona/Mahodari (India).
It does not seem to have been found in France but it is the surely present being given frequency of the weathered basalts known in France.
The type of this species and its location are not definable.
HISTORY : Name inspired from the Greek word "επι" [epi] meaning "almost" and from "σiτλβεν" [stilbein] meaning "sparkling"
Species described in 1826 by Gustav Rose (1798-1873), German mineralogist
Type-locality: Teigarhorn, Berufjördur, Iceland
CHEMICAL FORMULA : Ca Al2 Si6O16 5H2O
CRYSTAL SYSTEM : Monoclinic
COLOR : Colorless, white, pinkish yellowish
DIAPHANIETY : Transparent to translucent
LUSTER : Vitreous
STREAK : White
MORPHOLOGIE : Tabular crystals, prismatic. Radial aggreagates
HARDNESS : 4
CHEMICAL CLASS: 2,266
DENSITY : VIII - Silicates
GROUP : Mordenite-bikitaite series
STRUNZ CLASS BEFORE 2001 : 8/J.22-40
STRUNZ CLASS AFTER 2001 : 9.GD.05
