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Figure 4
Drawing parallels between the danburite-II crystal structure and an ideal h.c.p. structure. (a) A view of an h.c.p. structure based on hexagonal cubo­octahedra (shown in green). A void with trigonal–bipyramidal geometry is shown in yellow. (b) A representation of the crystal structure of danburite-II based on a distorted h.c.p. structure made of Ca and O atoms. CaO11 polyhedra (defective hexagonal cubo­octahedra) are shown in green. The void with trigonal–bipyramidal geometry is occupied by an Si atom (shown in black). The bright-green sphere towards the top centre of panel (b) represents the B atom occupying a tetrahedral void.

Volume 4| Part 5| September 2017| Pages 671-677
ISSN: 2052-2525