Schullerite, Ba2Na(Mn,Ca)(Fe3+,Mg,Fe2+)(2)Ti-2(Si2O7)(2)(O,F)(4), a new mineral species from the Eifel volcanic district, Germanyстатья
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Аннотация:A new heterophyllosilicate mineral schullerite was found in the Lohley basalt quarry in the Eifel volcanic region, Germany, as a member of the late mineral assemblage comprising nepheline, leucite, augite, phlogopite, magnetite, titanite, fresnoite, barytolamprophyllite, fluorapatite, perovskite, and pyrochlore. Flattened brown crystals of schullerite up to 0.5 x 1 x 2 mm in size and their aggregates occur in miarolic cavities of alkali basalt. The mineral is brittle, with a Mohs hardness 3-4 and perfect cleavage parallel to (001). D (calc) = 3.974 g/cm(3). Its IR spectrum is individual and does not contain bands of OH-, CO (3) (2-) or H2O. Schullerite is biaxial (-), alpha = 1.756(3), beta = 1.773(4), gamma = 1.780(4), 2V (meas) = 40(20)A degrees. Dispersion is weak, r < nu. Pleochroism is medium X > Y > Z, brown to dark brown. Chemical composition (electron microprobe, mean of five-point analyses, Fe2+/Fe3+ ratio determined by the X-ray emission spectroscopic data, wt %): 3.55 Na2O, 0.55 K2O, 3.89 MgO, 2.62 CaO, 1.99 ArO, 28.09 BaO, 3.43 FeO, 8.89 Fe2O3, 1.33 Al2O3, 11.17 TiO2, 2.45 Nb2O5, 26.12 SiO2, 2.12 F, -0.89 -O=F-2, 98.98 in total. The empirical formula is (Ba1.68Sr0.18K0.11Na1.05Ca0.43Mn0.47Mg0.88Fe (0.44) (2+) Fe (1.02) (3+) Ti1.28Nb0.17Al0.24)(I 7.95)Si3.98O16.98F1.02 pound. The crystal structure was refined on a single crystal. Schullerite is triclinic, space group P1, unit cell parameters: a = 5.4027(1), b = 7.066(4), c = 10.2178(1), alpha = 99.816(1), beta = 99.624(1), gamma = 90.084(1)A degrees, V = 378.75(2) (3), Z = 1. The strongest lines of the X-ray powder diffraction pattern [d, , (I, %)]: 9.96(29), 3.308(45), 3.203(29), 2.867(29), 2.791(100), 2.664(46), 2.609(36), 2.144(52). The mineral was named in honor of Willi Schuller (born 1953), an enthusiastic, prominent amateur mineral collector, and a specialist in the mineralogy of Eifel. Type specimens have been deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, registration no. 3995/1,2.