
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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28  Structure matters  FCC packing 
