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Figure 5
Representation of the crystal structure of danburite-II on the basis of the close-packing approach. (a) The arrangement of octahedral voids in the packing of O (red) and Ca (blue) atoms in danburite-II, featuring chains of edge-sharing octahedral voids parallel to the c axis. The area outlined by the dashed line is magnified in panel (b). (b) Four chains of edge-sharing octahedral voids making up adjacent c.c.p. and h.c.p. blocks. (c) A scheme showing the origin of the `square contact' between the c.c.p. and h.c.p. blocks through the cover of underlying double chains of octahedra by octahedra in either a c.c.p. (lilac octahedron) or h.c.p. (green octahedron) fashion.

IUCrJ
Volume 4| Part 5| September 2017| Pages 671-677
ISSN: 2052-2525
https://doi.org/10.1107/S2052252517010612