Pollucite

Pollucite is a zeolite mineral with the formula (Cs,Na)₂Al₂Si₄O₁₂·2H₂O 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, with a brittle fracture and no cleavage.

Pollucite
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
Category	Zeolite group, tectosilicate
Formula (repeating unit)	Cs(Si2Al)O6·nH2O
IMA symbol	Pol[1]
Strunz classification	9.GB.05
Dana classification	77.1.1.2
Crystal system	Isometric
Crystal class	Hexoctahedral (m3m) H-M symbol: (4/m 3 2/m)
Space group	Ia3d
Unit cell	a = 13.67 Å; Z = 16
Identification
Color	Usually colorless; also white, grey, pink, blue or violet
Crystal habit	Usually massive; rare crystals are normally trapezohedral or cubic
Cleavage	None observed
Fracture	Conchoidal to uneven
Tenacity	Brittle
Mohs scale hardness	6.5 to 7
Luster	Vitreous to greasy
Streak	White
Diaphaneity	Transparent to translucent
Specific gravity	2.7 to 3.0
Optical properties	Isotropic or very weakly anisotropic
Refractive index	1.508–1.528
Solubility	Readily soluble in HF; dissolves with difficulty in hot HCl
Other characteristics	Sometimes weakly fluorescent under SW and LW UV
References	[2][3][4][5][6]

Discovery and occurrence

A pollucite ore sample 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).^[7] The high caesium content was missed by the first analysis by Karl Friedrich Plattner in 1848,^[8] but after the discovery of caesium in 1860 a second analysis in 1864 was able to show the high caesium content of pollucite.^[9]

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.^[10] This ore is about 23%^[11]: 1 to 25%^[12]: 2 caesium by weight.

References

1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
2. Mineralienatlas
3. Gaines, et al. (1997) Dana's New Mineralogy, Wiley ISBN 978-0471193104
4. Pollucite on Mindat.org
5. Pollucite data on Webmineral
6. Handbook of Mineralogy
7. Breithaupt, August (1846). "Neue Mineralien". Annalen der Physik und Chemie. 69 (11): 439–442. Bibcode:1846AnP...145..429B. doi:10.1002/andp.18461451111.
8. Plattner, C. F. (1846). "Chemische Untersuchung zweier neuen, vom Herrn Prof. Breithaupt mineralogisch bestimmten Mineralien von der Insel Elba". Annalen der Physik und Chemie. 145 (11): 443–447. Bibcode:1846AnP...145..443P. doi:10.1002/andp.18461451112.
9. Pisani, F. (1864). "Étude chimique et analyse du pollux de l'ile d'Elbe". Comptes rendus. 58: 714–716.
10. http://www.encyclopedia.com/doc/1G1-75752682.html Original reference to Mining Journal, March 2, 2001, p 160. Accessed March 28, 2009. (dead link 15 February 2022)
11. Harris, Keith L. (1979). Cesium. US Department of the Interior, Bureau of Mines.
12. Nichols, Ivan L.; Dean, Karl C. (1966). Volatilization of Cesium Chloride from Pollucite Ore. Vol. 6780. US Department of the Interior, Bureau of Mines.