A first natural occurrence of triclinic sincosite, Ca(VO)(2)(PO4)(2 center dot)4H(2)O, from the South Rasmussen Ridge Mine, Idaho, USA

摘要

A single-crystal structure analysis of sincosite from the South Rasmussen Ridge mine, Idaho, USA has confirmed it as the first natural occurrence with triclinic symmetry. Previous work on the mineral, based on limited electron diffraction and single crystal studies, together with the indexing of powder X-ray diffraction data, have described it as having tetragonal symmetry; although hydrothermally prepared synthetic sincosite is triclinic. The unit cell parameters are a = 6.3531(12), b = 6.3567(14), c= 6.6050(18) angstrom, alpha = 106.995(22), beta = 94.115(19), gamma = 90.006(16)degrees, and the space group is P1. The crystal structure was refined to wR(obs) = 0.11 for 783 reflections with I > 4 sigma(1). The structure refinement and electron probe micro analysis both confirm the composition as Ca(VO)(2)(PO4)(2)center dot 4H(2)O.