In geometry, the elongated hexagonal dipyramid is constructed by elongating a hexagonal dipyramid (by inserting a hexagonal prism between its congruent halves.
This polyhedron is in the family of elongated dipyramids, of which the first three can be Johnson solids: J14, J15 and J16. The hexagonal form can be constructed by all regular faces, but isn't a Johnson solid because 6 equilateral triangles would form six co-planar faces (in a regular hexagon).
- A quartz crystal is an example of an elongated hexagonal dipyramid. Because it has 18 faces, it can be called an octadecahedron.
- The edge-first orthogonal projection of a 24-cell is an elongated hexagonal dipyramid.