Beryllonite 2959723 147876933 2007-07-29T16:45:19Z CSWarren 567897 Fixing [[Wikipedia:Disambiguation pages with links|links to disambiguation pages]] using [[Project:AutoWikiBrowser|AWB]] '''Beryllonite''' is a rare [[sodium]] [[beryllium]] [[phosphate mineral]] with formula NaBePO<sub>4</sub>. The tabular to prismatic [[monoclinic]] crystals vary from colorless to white or pale yellowish, and are transparent with a vitreous [[Lustre (mineralogy)|lustre]]. [[Crystal twinning|Twinning]] is common and occurs in several forms. It exhibits perfect [[cleavage (crystal)|cleavage]] in one direction. The [[Mohs scale of mineral hardness|Hardness]] is 5.5 to 6 and the [[specific gravity]] is 2.8. [[Refractive index|Refractive indices]] are nα = 1.552, nβ = 1.558 and nγ = 1.561. A few crystals have been cut and [[facet]]ed, but, as the refractive index is no higher than that of quartz, they do not make very brilliant [[gemstone]]s. It occurs as a secondary beryllium mineral in granitic and alkalic [[pegmatite]]s. It was first described from complex crystals and as broken fragments in the disintegrated material of a [[granitic]] vein at [[Stoneham, Maine]], where it is associated with [[feldspar]], smoky [[quartz]], [[beryl]] and [[columbite]]. It was discovered by [[James Dwight Dana]] in 1888, and named beryllonite for its beryllium content. ==References== *Palache, C., H. Berman, and C. Frondel (1951) Dana’s system of mineralogy, (7th edition), v. II, pp. 677–679 *[http://www.mindat.org/min-644.html Mindat with location data] *[http://www.webmineral.com/data/Beryllonite.shtml Webmineral data] *{{1911}} [[Category:Beryllium minerals]] [[Category:Phosphate minerals]]