The crystal structure of takeuchiite, Mg 1. 71 Mn 1. 2 9BO 5 Acombinedsingle crystal X-ray and HRTEM study

Crystalsof the mineral takeuchiite, Mg1.5 9Mn 1.2of eO.lgBO s were investigatedby X-ray diffraction and high resolution electron microscopy (HREM)techniques. The space group is Pnnm, Z = 24, with the unit cell dimensionsa = 27.585(4), b = 12.561(3) and c = 6.027(2) A. The structural P.lodel previously derived from HREM studies was refined versus the 1492 most significant X-ray reflections to an R value of 0.063. The crystal structure can be interpreted as a chemical twinning of the basic structure typepinakiolite. As for other members of this structural family some of thecation positions are disordered.