Pollucite

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 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.