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The stilbite subgroup of the
zeolite group has members:
barrerite: Na2(Si7Al2)O18.6H2O
stilbite-Ca: NaCa4(Si27Al9)O72
.28H2O
stilbite-Na: Na9(Si27Al9)O
72.28H2O
stellerite: Ca4(Si28Al8)O72.28H2O
Stilbite is found in cavities in basalt and related rocks, associated with
heulandite, chabazite and other
zeolites and calcite.
Geothermal wells have been drilled through a thick series of basalt flows in western Iceland, where it was found that
stilbite crystallised at temperatures from 75oC to 200oC at depths between 45m and 1200m
(ZW).
Stilbite is relatively frequent in crevices in metamorphic rocks, sometimes associated with
quartz, epidote,
prehnite and K-feldspar variety adularia.
Localities
At High Force Quarry, Forest and Frith, County Durham, England, UK, crystals of stilbite line closely spaced open fissures up to
3 mm wide in chloritised dolerite pegmatite. The
stilbite is accompanied by small crystals of analcime and
chabazite
(JRS 21.14).
At the Copper Falls Mine, Copper Falls, Keweenaw county, Michigan, USA, mineralisation occurs primarily in hydrothermal veins
cutting preexisting lavas and as amygdules in the Ashbed flow.
Stilbite is one of the rarer zeolites in the Keweenaw Peninsula. The Copper Falls
mine has produced what are probably the finest stilbites known from the Lake Superior District. Several specimens with
orangish crystals to 3 cm, some of them associated with calcite, are in the collection of
the A E Seaman Mineral Museum
(MinRec 54.1.113).
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