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Formula: (Sr,Ca,Na)5(Si27Al9)O72.24H2O
Tectosilicate (framework silicate), heulandite subgroup,
zeolite group
Crystal System: Monoclinic
Specific gravity: 2.2 measured, 2.24 calculated
Hardness: 3 to 3½
Streak: White
Colour: White, colourless, red, yellow, brown, green
Environments
Plutonic igneous environments
Basaltic cavities
Heulandite-Sr is a low-temperature zeolite found in a wide variety of
geologic environments: volcanic rocks, metamorphic rocks,
pegmatites,
tuffs and deep-sea sediments
(Webmin).
Localities
At the type locality, the Campegli Mine, Campegli, Castiglione Chiavarese, Genoa, Liguria, Italy,
heulandite-Sr ocurs in fractures of gabbroic rocks
(Mindat).
Heulandite-Sr from the Campegli Mine -
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Whitesmith Mine, Strontian, Fort William and Ardnamurchan, Highland, Scotland, UK.
In the description below, the mineral is simply referred to as "heulandite". Quantitative chemical analysis showed
that twelve of the 60 analyses fall within the heulandite-Ba
composition field, the remaining seventy-two are heulandite-Sr.
Heulandite, not previously known from Strontian, was first found at the Whitesmith Mine in 1979. The specimens
display blocky colourless crystals up to about 8 mm in length, with a slightly pearly lustre, in cavities with
hexagonal 'nailhead' calcite, cubo-octahedral
pyrite and occasional brewsterite.
The next interesting discovery was made in 2003. A careful examination revealed several parallel-running
baryte veins containing numerous cavities lined with drusy
brewsterite, acicular brown
strontianite and very rare heulandite. About ten
heulandite specimens were collected, and the finest of these contained a large cavity lined with acicular
brown strontianite and a scattering of colourless coffin-shaped
heulandite crystals to about 4 mm.
In 2008, a small collapse on the south wall of the opencut afforded an opportunity to examine another mineralised
area. Numerous thin calcite veins run parallel to the local cleavage and
where the rock is folded, larger cavities and fractures lined with
brewsterite and occasional weathered
strontianite are present. Heulandite was found as small
inconspicuous crystals in and around an otherwise unremarkable calcite vein
up to about 25 mm wide. The vein comprised two calcite cheeks between 5 and
10 mm in thickness, which commonly met, but sometimes opened to produce a narrow central cavity lined with
calcite, pyrite,
brewsterite and heulandite.
Where the vein intersected perpendicular veins and fractures, larger cavities lined with
brewsterite, calcite and
heulandite occasionally developed, the best of these contained heulandite crystals up to 18 mm long
(JRS 11.80-86).
Heulandite-Sr from the Whitesmith Mine -
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