Formula: Ca3[Si18Al6O48].16H2O tectosilicate (framework
silicate), zeolite group
Specific gravity: 2.22 to 2.28
Hardness: 4 to 4½
Colour: Colourless, white, orange, red
Epistilbite occurs in cavities in silica-rich basalt and
associated with laumontite, heulandite
(DHZ 4 p385). It also occurs in
gneiss. No diagenetic epistilbite has been reported.
In Iceland epistilbite occurs in geothermal wells in basalt at 80 to 160oC (Dana).
Common impurities: Fe,Mg,Na,K
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