Beryllonite: Gemstone Information
Beryllonite is sodium beryllium phosphate, NaBePO4 and is a mineral of granite and alkali pegmatites. It forms pseudo-orthorhombic crystals in the monoclinic system with hardness 5.5–6, SG in the range 2.77–2.84, RI 1.552, 1.558 and 1.561 for the alpha, beta and gamma rays; the birefringence is 0.009. Crystals are biaxial negative. The dispersion is low at0.010. Faceted beryllonite is almost always transparent, colourless. The classic location for beryllonite is Stoneham, Maine, USA, where it occurs at Sugarloaf Mountain, Brazil. Beryllonite is inert under UV, but under Xrays there is a dark sky-blue fluorescence with slight phosphorescence. Other sources are Finland,Zimbabwe and Minas Gerais, Brazil. Some chatoyant specimens havebeen reported from Afghanistan.