Fig 2 - Nomenclature of the apatite supergroup minerals
The crystal structure of apatite, as seen along c . The unit cell is outlined. The M1-centred polyhedra are represented as six-fold coordinated metaprisms (the bonded O3 ligands are not included in this polyhedral representation). Two out of the seven bonds to M2 overlap in this projection, therefore only five are visible in the figure.