Phenakite: Gemstone Information
Phenakite is Be2SiO4 and occurs as transparent to translucent colourless rhombohedral, tabular to prismatic crystals of the trigonal system with hardness 7.5–8 and SG 2.93–3.00. The RI for the ordinary and extraordinary rays is 1.650–1.656 and 1.667–1.670, uniaxial positive with birefringence 0.016. Coloured specimens result from surface staining. Various fluorescence effects have been reported under UV and under X-rays specimens show a distinct blue. The occasional chatoyant specimen is reported;four-rayed star stones with a brownish tint are reported from Sri Lanka.Phenakite occurs in granite pegmatites and fine crystals have been found at the São Miguel de Piracicaba east of Belo Horizonte, Minas Gerais, Brazil,and at Amelia, Virginia, US. Fine crystals also occur along the Takovaya River near Ekaterinburg, Russia. Phenakite crystals occurring as inclusions in emerald usually indicate man-made origin.