Pollucite

pollucite [pə′lü‚sīt]

(mineralogy)

(Cs,Na)₂Al₂Si₄O₁₂·H₂O A colorless, transparent zoolite mineral composed of hydrous silicate of cesium, sodium, and aluminum, occurring massive or in cubes; used as a gemstone. Also known as pollux.

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Pollucite 

a mineral, a hydrous aluminosilicate of the composition (Cs, Na) [AlSi₂O₆]·_nH₂O. Pollucite contains 26–32 percent Cs₂O and admixtures of Rb₂O, K₂O, and Tl₂O. The crystal structure is basically an aluminosilicate framework of bonded SiO₄ and AlO₄ tetrahedrons; Cs⁺ and Na⁺ cations and zeolitic H₂O are arranged in the interstices of the framework. Pollucite crystallizes in the isometric system, generally forming dense masses and granular aggregates, as well as pockets, sometimes as large as 1 m in diameter; in hollows it occurs in the form of crystals. It has a hardness of 6.5 on Mohs’ scale and a density of 2,860–2,900 kgm³. Its color is white, occasionally light pink. Often the mineral is colorless and transparent. Physically it resembles quartz.

Pollucite occurs in granitic pegmatites in association with other minerals. It serves as a primary ore of metallic cesium and its salts.