Poudrettite: Gemstone Information

Poudrettite is KNa2B3Si12O30 and forms transparent violet to pink roughly equant barrel-shaped prismatic crystals of the hexagonal system with hardness about 5 and SG 2.51–2.53. The RI for the ordinary and extraordinary rays is 1.511 and 1.532, uniaxial positive with birefringence 0.021.Poudrettite is found at Mt Saint Hilaire, Quebec, Canada, in marble xenoliths within nepheline syenite breccias in an intrusive alkalic gabbro-syenite complex. Violet crystals with strong purple-pink to colourless to light brown pleochroism are reported from the Mogok area of Myanmar.