PHYSICAL PROPERTIES:
Chemistry: NaCa2Al5Si13O36
-14H2O
Composition: Hydrated sodium
calcium aluminum silicate
Class: Silicates
Subclass: Tectosilicate
Group: Zeolites
Crystal system: monoclinic
Color: pink to red also
white or tinted yellow
Fracture: uneven
Hardness: 3.5 - 4
Specific gravity: 2.2
Refractive Index:
Pleochroism:
Luster: vitreous to pearly
Streak: white
Cleavage: perfect in the direction parallel
to the prominant pinacoid
Transparency: transparent but most often
translucent
Associated Minerals: apophyllite,
babingtonite, calcite, heulandite, natrolite, other zeolites
and quartz
COMPOSITION:
Hydrous calcium, sodium, aluminum silicate (1.4% Na2O,
7.7% CaO, 16.3% Al203,
57.4% SiO2, 17.2% H2O).
ENVIRONMENT:
Stilbite is a commonly found zeolite, that forms nice crystals
inside the bubbles and fisures of volcanic rocks that have undergone
a small amount of metamorphism.
CRYSTAL DESCRIPTION:
Stilbite and a related zeolite called stellerite, have
a clasic crystal structure. Their crystals are commonly intergrown to
form a structure resembling wheat sheafs. This hourglass structure looks
like several crystals stacked next to each other with the tops and bottoms
fanning out while the middle remains thin. Stilbite is sometimes found
to have rounded knobs with radiating structures and twins may also be
found. Stilbite has a typical zeolite openness that allows large ions
and molecules to reside and actually move around inside the overall
framework.
DISTINGUISHING CHARACTERISTICS:
Whether in the wheat sheafs or not, stilbite can
be a hansome specimen, with it's high luster
and pearly cleavage faces. It may be yellow, brown, reddish, white.
The larger and sheaf-like crystals are sufficiently typical to distinguish
stilbite from the other common zeolites.
TESTS:
Flame Test: Stilbite swells and writhes like heulandite, but the
protuberances are more worm like. When fusing, the worms are more splintery
than heulandite. Apophyllite boils and melts to droplets with less swelling.
LOCALITIES:
Excellent specimens have come from the Paterson district of New Jersey.
Nova Scotia has an abundance of the mineral, found in the Annapolis
Valley region along the Bay of Fundy. Bright orange crystals have been
found at Great Notch, New Jersey, and Kilpatrick, Scotland. Today we
are acquiring many wonderfull specimens from Poona, India and other
areas near this local.
USES:
Mineral specimens and chemical filter. Zeolites, including
stilbite, can absorb up to 30 per
cent of their dry weight in gasses and 90 per cent in hydrocarbons.
This allows the mineral
to be used in oil spill clean-ups and in other industrial processes
because of its ability to
absorb odour and suppressants. Another capability of stilbite is the
ability to attract calcium and magnesium so that it can be used in water
softening.
FACTS & HISTORY:
From the Greek stilbe - "luster" in allusion to the pearly to vitreous
luster.
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