Simple hexagonal (HP) structure elements .
Am, Bk, C (graphite), Cf, Cm .
. .
Crystal lattice .
     The crystal lattice of HP elements can be modeled as shown previously for the HP
sphere packing where hexagonal prisms stack together in an eclipsed arrangement.
     Graphite has a special type of HP structure where the layers of hexagonal prisms
stack together in a staggered formation, as shown in the following image.  In this
arrangement the hexagonal rings of carbon atoms in adjacent vertical layers are
staggered relative to each other, but alternating layers eclipse each other.


     Figure 50 -  Graphite lattice structure
                           click image to enlarge
Polyhedral framework (graphite)  


     Figure 51 -  Polyhedral framework
                  model of graphite
             ( 40 T, 42 S, 106 pinges )
                         click image to enlarge
     The polyhedral framework demonstrates that the graphite structure can be viewed  
as two interpenetrating lattices (pictured red and blue here) with each cell of each
lattice comprised of two hexagonal prisms stacked on top of each other.  The carbon
atoms are located at the corner vertices of these elongated HP cells.  Notice the
shorter bond length between atoms of adjacent layers that eclipse each other
compared to atoms of alternate layers that are eclipsed.  One half of the bonds
between atoms in the different layers are these longer bonds.  This causes weakness
in the bond strength between atoms of different layers compared to the bond strength
of atoms within the same layer.  As a result the separate layers to tend to slip past
each other. This accounts for graphite's excellent lubricant properties and its softness
as a marker.
Cleavage (graphite)
     (100) - perfect and easy - the result of the relatively weaker inter-layer bonds
Crystal habit (graphite)
     tablets, scaly

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