Face centered cubic packing (FCC) .
     In contrast, adding a third triangulated layer of spheres to the existing two layers
so that none of the spheres of the three layers eclipse each other results in the face .
centered cubic (FCC) packing arrangement.   Due to the vertical staggering of the .




( 24 T, 12 pinges)

overhead view



click image to enlarge



Figure 39 - Face centered cubic (FCC) sphere packing

spheres in all three layers the arrangement is referred to as ABC.  Like the HCP .
packing, each sphere in the FCC packing is twelve coordinated.  However due to .
the staggered arrangement of the thirteen  sphere array the sphere centers lie on .
the vertices of a regular cuboctahedron.  .
     Notice in particular that the triangulated layers of close packed spheres in the
HCP "twist" cuboctahedron are aligned parallel to each other.  In contrast, the FCC
cuboctahedron cluster is demonstrated to possess four intersecting layers of closest
packed spheres that correspond to the four (111) planes of cubic symmetry.  As a
result the FCC cuboctahedron cluster of spheres possess full cubic symmetry with
nine mirror planes and seven axes of rotational symmetry.  In contrast, the "twist"
cuboctahedron cluster has only four mirror planes and seven axes of rotational
symmetry.  Therefore the FCC sphere packing and lattice is demonstrated to be
inherently more symmetrical than the HCP packing.
     Since the spheres of both the HCP and FCC arrangement are closest packed they
both can be modeled as a CCP lattice, that is, a space filling of tetrahedra and
octahedra in the ratio of 2:1 respectively.

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Page  28 -  Structure matters - FCC packing

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