Electron microscopy of oxyborates. III. On the structure of takéuchiite

The crystal structure of the new mineral takéuchiite, Me₃BO₅ (Me = Mg, Mn²⁺, Mn³⁺, Fe³⁺, Ti⁴⁺), has been derived by matching experimentally obtained high-resolution transmission electron microscope images with computed ones. The crystals are orthorhombic Pnnm or Pnn2, with a= 27.50 (1), b = 12.614 (2) and c = 6.046 (1) Å and Z = 24. The structure can be described as a periodic chemical twinning of the parent structure of pinakiolite, and is thus closely related to the other known chemical twins of pinakiolite, viz ludwigite and orthopinakiolite.