Lucchesiite, CaFe32+Al6(Si6O18)(BO3)(3)(OH)(3)O, a new mineral species of the tourmaline supergroup

摘要

Lucchesiite, CaFe32+Al6(Si6O18)(BO3)(3)(OH)(3)O, is a new mineral of the tourmaline supergroup. It occurs in the Ratnapura District, Sri Lanka (6 degrees 35'N, 80 degrees 35'E), most probably from pegmatites and in Mirosov near Strazek, western Moravia, Czech Republic, (49 degrees 27'49.38"N, 16 degrees 9'54.34"E) in anatectic pegmatite contaminated by host calc-silicate rock. Crystals are black with a vitreous lustre, conchoidal fracture and grey streak. Lucchesiite has a Mohs hardness of similar to 7 and a calculated density of 3.209 g/cm(3) (Sri Lanka) to 3.243 g/cm(3) (Czech Republic). In plane-polarized light, lucchesiite is pleochroic (O = very dark brown and E = light brown) and uniaxial (-). Lucchesiite is rhombohedral, space group R3m, a approximate to 16.00 angstrom, c approximate to 7.21 angstrom, V approximate to 1599.9 angstrom(3), Z = 3. The crystal structure of lucchesiite was refined to R1 approximate to 1.5% using similar to 2000 unique reflections collected with MoKa X-ray intensity data. Crystal-chemical analysis for the Sri Lanka (holotype) and Czech Republic (cotype) samples resulted in the empirical formulae, respectively: (X)(Ca0.69Na0.30K0.02)(Sigma 1.01)(Y)(Fe1.442+Mg0.72Al0.48Ti0.334+V0.023+Mn0.01Zn0.01)(Sigma 3.00)(Z)(Al4.74Mg1.01Fe0.253+)(Sigma 6.00) [(T)(Si5.85Al0.15)S6.00O18](BO3)(3)(V)(OH)(3)(W)[O0.69F0.24(OH)(0.07)](Sigma 1.00) and (X)(Ca0.49Na0.45.square K-0.05(0.01))(Sigma 1.00) (Y)(F-1.14(e2+) Fe-0.95(3+) Mg0.42Al0.37 Mn0.03Ti0.084+Zn0.01)(Sigma 3.00)(Z)(Al-5.11 Fe-0.38(3+) Mg-0.52)(Sigma 6.00) [(T)(Si5.88Al0.12)(Sigma 6.00)O-18] (BO3)(3) (V)[(OH)(2.66)O-0.34]Sigma(3.00) (W)(O0.94F0.06)(Sigma 1.00).