The crystal structure of yoshimuraite, a layered Ba-Mn-Ti silicophosphate,with comments on five-coordinated Ti4+

The crystal structure of yoshimuraite, ideally Ba2Mn2TiO(Si2O7)(PO4)(OH), h as been determined and refined to residuals of R = 3.0% and wR = 4.1% using material from the Taguchi mine, Aichi Prefecture, Honshu, Japan. It is tri clinic, P (1) over bar, with cell parameters a 5.386(1), b 6.999(1), c 14.7 48(3) Angstrom, alpha 89.98(1), beta 93.62(2), gamma 95.50(2)%, V 552.3(1) Angstrom(3), with Z = 2. The mineral is strongly layered on (001), consisti ng of two quasi-tetrahedral layers composed of TiO5 polyhedra cross-linked by corner-sharing (Si2O7) clusters. These layers bound on two sides a layer of closest-packed Mn phi(6) octahedra, thus forming a composite unit remin iscent of that found in 2:1 phyllosilicates. Such composite units are subse quently linked along [001] via an interlayer-like [Ba-2(PO4)] sheet, the bo nding between the two being relatively weak and resulting in the pronounced {001} cleavage observed in the mineral. Yoshimuraite is a member of the BM n heterophyllosilicate polysomatic series [specifically, the BMo polysome s eries], which includes phases such as astrophyllite, bafertisite and seidoz erite.