Scandiobabingtonite, a new mineral from the Baveno pegmatite, Piedmont, Italy

Scandiobabingtonite, ideally Ca-2(Fe2+,Mn)ScSi5O14(OH) is the scandium anal ogue of babingtonite; it was found in a pegmatitic cavity of the Baveno gra nite associated with orthoclase, albite, muscovite, stilbite, and fluorite. Its optics are biaxial (+) with 2V = 64(2)degrees, alpha = 1.686(2), beta = 1.694(3), gamma = 1.709(2). D-meas = 3.24(5) g/cm(3), D-calc = 3.24 g/ cm (3), and Z = 2. Scandiobabingtonite is colorless or pale gray-green, transp arent, with vitreous luster. It occurs as submillimeter sized, short, tabul ar crystals, slightly elongated on [001], and characterized by the associat ion of forms {010}, {001}, {110}, {<1(1)over bar>0}, and {101}. It occurs a lso as a thin rim encrusting small crystals of babingtonite. The strongest lines in the X-ray powder pattern are at 2.969 (S), 2.895 (S), 3.14 (mS), a nd 2.755 (mS) A. The mineral is triclinic. space group Pr, with a = 7.536(2 ), b = 11.734(2), c = 6.748(2) Angstrom, alpha = 91.70(2), beta = 93.86(2), gamma = 104.53(2)degrees. Scandiobabingtonite is isostructural with babing tonite, with Sc replacing Fe3+ in sixfold coordination, but no substitution of Fe2+ by Sc takes place. Due to the lack of a suitably large crystal of the new species, such a replacement has been confirmed by refining the crys tal structure of a Sc-rich babingtonite (final R = 0.047) using single-crys tal X-ray diffraction (XRD) data.