The Crystal Structure of Ludlamite

The structure of ludlamite has been determined using X-ray methods (Weissenbcrg and oscillation photographs, MoKα, λ=0.71Å) . The material used is from the Ashio mine. Tochigi pref., Japan and has the composition, Fe3 (PO4) 2⋅4H2O (analysed by H. Minato, 1948) . The unit cell has the dimensions, a=10.45Å, b=4.65Å, c=9.35Å, β=79'27, containing two molecules of Fe3 (PO4) 2⋅4H2O. The space group is C _??_2h-P21/α, the reflexions (h0l) and (0k0) being absent respectively when Ii and I are odd. In the structure, each P atom is in the middle of a more or less distorted tetrahedron formed by oxygen atoms and one Fe atom occupie the center of an octahedron formed by six oxygen atoms and the other Fe that of an octahedron formed by three oxygen atoms and three H2O molecules. An FeO6 octahedron and two PO4 tetrahedra. form a complex group holding O-O edges in common. This FeP2O10 group in turn forms a chain stretched indefinitely in the direction of the b-axis, sharing oxygen atoms with the adjoining similar groups. H2O groups occupy the interstices left vacant by these larger groups of atoms. Each oxygen atom is shared by one P and one or two Fe atoms and H2O by one or two Fe atoms.