Rinkite: Gemstone Information
Rinkite is (Ca,Ce)4Na(Na,Ca)2Ti(Si2O7)2F2(O,F)2 and forms opaque to translucent reddish brown masses in the monoclinic system with hardness 4–5 and SG 3.18–3.44. The RI for the alpha, beta and gamma rays is 1.643–1.662, 1.645–1.667 and 1.651–1.681, biaxial positive with birefringence 0.009. Absorption lines have been recorded at 878, 806,749, 743, 683, 585, 527 and 513 nm. Rinkite occurs in nepheline syenites and related pegmatites. Gemstones have been fashioned from specimens collected at sites at the Khibiny massif on the Kola Peninsula, Russia.