On the crystal structure of pseudowollastonite (CaSiO 3 )

Nine tourmaline crystals for which major and minor element composition data are available have been examined by single-crystal X-ray structure refinement. The single crystals were then analyzed for major elements (by electron microprobe methods), Fe 3 /Fe 2+ (by synchrotron micro- X-ray absorption near-edge spectroscopy). B and Li (by secondary ion mass spectrometry), and bulk H content (by uranium extraction). Despite recent claims based on chemical analyses, struc­ture analysis suggests that no B exists in tetrahedral coordination in these samples. Analysis of cation ordering between the Y and Z octahedral sites suggests that the occurrence of an Fe 2+ atom on a Y octahedral site may be locally associated with the absence of Mg at both of the neighboring Z sites, as substitutions of Fe 2+ on Y and Mg on Z require antithetic shifts of the O6 anion.