Chemistry:Pollucite

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Pollucite
Pollucite-193819.jpg
Euhedral, tabular crystal of colorless, translucent and lustrous pollucite with frosted crystal faces from Afghanistan (size: 2.7 x 2.4 x 1.2 cm)
General
CategoryZeolite mineral
Formula
(repeating unit)
Cs(Si
2
Al)O
6
 · nH
2
O
Strunz classification9.GB.05
Dana classification77.1.1.2
Crystal systemIsometric
Crystal classHexoctahedral (m3m)
H-M symbol: (4/m 3 2/m)
Space groupIa3d
Unit cella = 13.67 Å; Z = 16
Identification
ColorUsually colorless, also white, grey, pink, blue or violet
Crystal habitUsually massive, rare crystals are normally trapezohedral or cubic
CleavageNone observed
FractureConchoidal to uneven
TenacityBrittle
Mohs scale hardness6.5 to 7
|re|er}}Vitreous to greasy
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity2.7 to 3.0
Optical propertiesIsotropic or very weakly anisotropic
Refractive index1.508-1.528
SolubilityReadily soluble in HF, dissolves with difficulty in hot HCL
Other characteristicsSometimes weakly fluorescent under SW and LW UV
References[1][2][3][4][5]

Pollucite is a zeolite mineral with the formula (Cs,Na)
2
Al
2
Si
4
O
12
 · 2H
2
O
with iron, calcium, rubidium and potassium as common substituting elements. It is important as a significant ore of caesium and sometimes rubidium. It forms a solid solution series with analcime. It crystallizes in the isometric - hexoctahedral crystal system as colorless, white, gray, or rarely pink and blue masses. Well formed crystals are rare. It has a Mohs hardness of 6.5 and a specific gravity of 2.9. It has a brittle fracture and no cleavage.

Discovery and occurrence

Another sample of Pollucite Ore, held in the Royal Ontario Museum

It was first described by August Breithaupt in 1846 for occurrences on the island of Elba, Italy. It is named for Pollux, the twin of Castor on the grounds that it is often found associated with petalite (previously known as castorite).[6] The high caesium content was missed by the first analysis by Karl Friedrich Plattner in 1848,[7] but after the discovery of caesium in 1860 a second analysis in 1864 was able to show the high caesium content of pollucite.[8]

Its typical occurrence is in lithium-rich granite pegmatites in association with quartz, spodumene, petalite, amblygonite, lepidolite, elbaite, cassiterite, columbite, apatite, eucryptite, muscovite, albite and microcline.

About 82% of the world's known reserves of pollucite occur near Bernic Lake in Manitoba, Canada, where they are mined for their caesium content for use in caesium formate oil drilling assistance.[9] This ore is about 20% by weight caesium.

References