Pollucite

minerals

perhamite

montebrasite

lepidolite

Formula: Cs(Si2Al)O6.nH2O
Tectosilicate (framework silicate), zeolite, forms solid solutions with analcime and with leucite (R&M 94.5.420-425).
Specific gravity: 2.67 to 3.03
Hardness: 6½ to 7
Streak: White
Colour: Colourless, white, grey, pink, blue, violet
Solubility: Slightly soluble in hot hydrochloric acid; readily soluble in HF
Environments:

Pegmatites

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 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.
Common impurities: Fe,Ca,K,Rb

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