La structure cristalline de la defernite (original) (raw)

Defernite, a new mineral with an unusual structure is orthorhombic: Pnam, a= 17.860 (5), b 22.775 (6) and c 3.658 (1) Â. V 1487.9 Â2, Z 4, Dx 2.42, Dm 2.5 g/cm3. The structure was solved by direct methods and the use of the Fourier difference map. From the counter diffractometer data, the structure was refined isotropically to a final Rw of 0.082, whereas the final R( was 0.142. Probably the refinement could not be persued further due to the quality of the crystal and because the structure of the mineral contains weakly bound water molecules difficult to locate and shows occasional replacement of (C03)2 or (OH)"1. In relation to the structure the difficulty of the analysis of a carbonate mineral by microprobe is discussed. The structure is formed along axis a, of ribbons, composed of CaOy (OH)x polyhedra surrounding the (C03)"2 groups and along axis c, of and along axis c, of infinite channels in which water molecules could be located. Keywords .-Defernite, structure.