JERVISITE, NaScSi2O6: OPTICAL DATA, MORPHOLOGY, RAMAN SPECTROSCOPY, AND CRYSTAL CHEMISTRY

The crystal structure of jervisite, ideally NaScSi2O6, was refined using single-crystal X-ray data collected using a crystal from the Seula quarry (Baveno, Verbano-Cusio-Ossola province, Italy). The refinement was carried out in the C2/c space group giving the following unit-cell dimensions: a¼9.8478(2) A? , b¼9.0575(1) A? , c¼5.3409(3) A? , b¼106.87(2)8, and V¼455.89(2) ?A 3 for Z¼4. The previous crystal structure, refined using data from a synthetic analogue and a natural sample, was confirmed and conforms with that of aegirine. The bond-valence calculation and the refined occupancy of the M1 and M2 sites confirm the cation distribution adopted in the empirical formula. Raman spectroscopy and refractive index measurements were also performed, and the morphology was studied in order to provide a complete description of this Sc-bearing Na pyroxene.