Abstract

Scandiobabingtonite, ideally Ca 2 (Fe (super 2+) ,Mn)ScSi 5 O 14 (OH) is the scandium analogue of babingtonite; it was found in a pegmatitic cavity of the Baveno granite 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, transparent, with vitreous luster. It occurs as submillimeter sized, short, tabular crystals, slightly elongated on [001], and characterized by the association of forms {010}, {001}, {110} {110-}, and {101}. It occurs also 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), and 2.755 (mS) Aa. The mineral is triclinic, space group P1, with a = 7.536(2), b = 11.734(2), c = 6.748(2) Aa, alpha = 91.70(2), beta = 93.86(2), gamma = 104.53(2) degrees . Scandiobabingtonite is isostructural with babingtonite, with Sc replacing Fe (super 3+) in sixfold coordination, but no substitution of Fe (super 2+) 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 crystal structure of a Sc-rich babingtonite (final R = 0.047) using single-crystal X-ray diffraction (XRD) data.

First Page Preview

First page PDF preview
You do not currently have access to this article.