Stilbite

minerals

heulandite

zeolite

chabazite

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The stilbite minerals are tectosilicates (framework silicates) and members of the zeolite group, being:
Stilbite-Ca: NaCa4(Si27Al9)O72 .28H2O
Stilbite-Na: Na9(Si27Al9)O 72.28H2O

Specific gravity: (both) 2.1 to 2.2,
Hardness: (both) 3½ to 4
Streak: (both) White
Colour: (both) White, Red, Yellow, Brown, Cream
Solubility: Moderately soluble in hydrochloric acid
Environments:

Basaltic cavities

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).

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