Petalite: Gemstone Information
Petalite is LiAlSi4O10 and forms transparent colourless tabular monoclinic crystals or masses. The hardness is 6.5 and there is one direction of perfect cleavage. The SG is 2.3–2.5 and the RI for the alpha, beta and gamma rays is 1.504–1.507, 1.510–1.513, 1.516–1.523, biaxial positive with birefringence 0.013. Some material may show an orange fluorescence. Petalite is a mineral of granite pegmatites where it may be found with other Li-minerals including spodumene and tourmaline group species. Faceted material is conspicuously limpid. Large crystals of facet quality have been produced at San Miguel de Paracicaba and elsewhere in Brazil. There have been reports of reddish specimens from Russia.