Vaterite: Interpretation in terms of OD theory and its next of kin

摘要: The polytypic structures of vaterite, CaCO 3 , described in recent literature, have been reinterpreted terms the order-disorder (OD) theory, which allows us to explain and systematize all observed predicted polytypes mineral a unified fashion. In this structure consists OD layers that comprise layer calcium coordination polyhedra attached halves standing CO groups. two-sided group symmetry is c 2/ m whereas interlayer operations are three twofold rotation axes at 120° one another, as well mirror plane common boundaries partial glide planes perpendicular boundary. Depending on orientation active axis with respect above-defined mesh, performed independently each stacking step, maximally ordered simple sequences P 6 1 22, 5 C 2 / more complicated sequence or 2, several disordered obtained (before eventual relaxation subgroup particular space group). A perfect copy vaterite occurs bastnasite-synchysite polysomatic series fluorocarbonates. these structures, REE layers, configurationally analogous Ca-based layer, p 32 their does not lead polytypism phenomena; generated layers.