Tris(o-phenylenedioxy)cyclotriphosphazine can induce a shift to this structure in other molecules by promoting clathration.  Martensitic transitions to this structure occur in shape metal alloys, and coarse-grained metals with this structure are prone to deformation twinning.  Compression along the C-axis in iron and zinc causes them to deviate more severely from the ideal form of this structure than magnesium, which has a nearly perfect c/a rati
Tris(o-phenylenedioxy)cyclotriphosphazine can induce a shift to this structure in other molecules by promoting clathration.  Martensitic transitions to this structure occur in shape metal alloys, and coarse-grained metals with this structure are prone to deformation twinning.  Compression along the C-axis in iron and zinc causes them to deviate more severely from the ideal form of this structure than magnesium, which has a nearly perfect c/a ratio of 1.624.  Because their axes are not orthogonal, these crystal structures are conventionally described by a four-axis system, Bravais-Miller indices.  Like the cubic system, this system has a close-packing crystal structure with a packing factor of 0.74.  For 10 points, name this crystal system used by hematite and graphite in which each atom has twelve equidistant neighbors.
Tris(o-phenylenedioxy)cyclotriphosphazine can induce a shift to this structure in other molecules by promoting clathration.  
hexagonal crystal system