Figure 3
The (2b) structure type, observed in M2(PO4)X minerals, where M = Mg2+ and X− = OH, F or M = Fe2+, Mn2+ and X− = OH. Two distinct arc-like configurations of F/O atoms are labelled up (U) and down (D). The example represents synthetic hydroxylwagnerite Mg2(PO4)OH (Raade & Rømming, 1986); hydrogen bonds (donor green, hydrogen black spheres) are shown as solid lines. |