The beautiful, electric blue tourmaline known a Paraiba Tourmaline from northeastern Brazil is generally elbaite to fluor-elbaite. A single point analysis by Beurlen et al. (2011) of a zoned schorl-elbaite crystal from the Carrascão pegmatite in quartzites that contain relic grains of multicolored elbaite, mostly replaced by lepidolite, found a composition that enters the rossmanite field.
[]=0.502
Na 0.486
Ca 0.01
References:
Beurlen H, de Moura OJM, Soares DR, Da Siliva MRR, Rhede D (2011) Geochemical and geological controls on the genesis of gem-quality "Paraiba Tourmaline" in granitic pegmatites from northeastern Brazil. The Canadian Mineralogist 49, 277-300.
last updated: 12-Jul-2014