| Pollucite | |
|---|---|
 Euhedral, tabular crystal of colorless, translucent and lustrous pollucite with frosted crystal faces fromAfghanistan (size: 2.7 x 2.4 x 1.2 cm) | |
| General | |
| Category | Tectosilicateminerals,zeolitegroup |
| Formula | 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/m3 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] |
Pollucite is azeolite mineral with the formula(Cs,Na)2Al2Si4O12·2H2O withiron,calcium,rubidium andpotassium as common substituting elements. It is important as a significant ore ofcaesium and sometimesrubidium. It forms a solid solution series withanalcime. It crystallizes in theisometric-hexoctahedral crystal system as colorless, white, gray, or rarely pink and blue masses. Well-formed crystals are rare. It has aMohs hardness of 6.5 and aspecific gravity of 2.9, with a brittle fracture and no cleavage.
It was first described byAugust Breithaupt in 1846 for occurrences on the island ofElba,Italy. It is named forPollux, the twin of Castor on the grounds that it is often found associated withpetalite (previously known ascastorite).[7] The high caesium content was missed by the first analysis byKarl 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 inlithium-rich granitepegmatites in association withquartz,spodumene,petalite,amblygonite,lepidolite,elbaite,cassiterite,columbite,apatite,eucryptite,muscovite,albite andmicrocline.
About 82% of the world's known reserves of pollucite occur nearBernic 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.
