Pollucite | |
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![]() 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 mineral |
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] |
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. It has a brittle fracture and no cleavage.