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Formula: Cs(Si2Al)O6.nH2O
Tectosilicate (framework silicate), zeolite, forms solid solutions with
analcime and with leucite
(R&M 94.5.420-425).
Crystal System: Isometric
Specific gravity: 2.9 measured, 2.96 calculated
Hardness: 6½ to 7
Streak: White
Colour: Colourless, white, grey, pink, blue, violet
Solubility: Slightly soluble in hot hydrochloric acid; readily soluble in HF
Common impurities: Fe,Ca,K,Rb
Environments:
Pollucite occurs only in the latest stages of crystallisation in the most evolved of the
lithium pegmatites. It is very
rare because of the paucity of cesium, Cs, in the Earth’s crust (4.5 ppm). It appears to crystallise near 400oC in most
of its occurrences
(R&M 94.5.420-425).
Associated minerals include quartz, spodumene,
petalite, amblygonite,
lepidolite, elbaite,
cassiterite, columbite,
apatite, eucryptite,
muscovite, K-feldspar,
albite and microcline
(HOM, Mindat).
The Tanco pegmatite at Bernic Lake ,Manitoba, Canada, contains an estimated 2,640 ppm Cs (compared with average 4.5 ppm in the
Earth's crust), and pollucite in vast deposits occurs here with beryl,
lepidolite and elbaite
(R&M 94.5.420-425).
The assemblages of minerals in the pegmatite were deposited in
succession from petalite + quartz to
spodumene + quartz to
eucryptite + quartz
(R&M 92.2.153).
The Koktokay number 3 pegmatite, Altai, northwest China, is a strongly zoned
spodumene-subtype pegmatite. Different types of pollucite occur here. First
is pollucite consisting of sodium- and cesium-enriched phases, which resulted
from local exsolution of primary pollucite. Next is nearly
end-member pollucite
that occurs as an aureole of primary pollucite in contact
with lepidolite or feldspar, and is formed
by dissolution and re-precipitation of primary pollucite. Then
pollucite associated with
quartz occurs in sub-parallel
veinlets penetrating surrounding albite crystals; this pollucite resulted
from replacement of
albite by cesium-rich fluids. Lastly in oscillatory-zoned pollucite,
typically restricted to the contact
of pollucite with small miarolitic cavities, the zonation compositionally oscillates about the cesium/sodium variations, and
is simply related
to locally changing fluid composition.
(AM 91.729-739).
The type locality is La Speranza, San Piero in Campo, Campo nell'Elba, Elba Island, Livorno Province, Tuscany, Italy.
At the Emmons pegmatite, Greenwood, Oxford county, Maine, USA, pollucite masses over one metre across occur in the core-margin
zone, cut by thin veinlets of lepidolite or
muscovite. Some veins have a core of analcime,
and thinner veins near the margin of the pollucite mass have perhamite,
fluorapatite and quartz. Pollucite is
usually associated with beryl, montebrasite
and spodumene. The Emmons pegmatite is an example of a highly evolved
boron-lithium-cesium-tantalum
enriched pegmatite
(R&M 94.6.513).
Alteration
quartz pseudomorphs after
pollucite have been found. Pollucite also
alters to analcime, K-feldspar variety
adularia,
lepidolite, spodumene and
clay.
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