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Polyhedral framework |
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The polyhedral framework model of FCC elements is identical to the lattice
model |
. |
which can be envisioned as the space filling of tetrahedra and octahedra in a
ratio of |
. |
2:1
shown previously. |
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Cleavage |
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The cleavage of a crystal refers to its tendency to be split apart along
certain |
. |
preferred planes which are often parallel to the orientation of its most
densely |
. |
packed layer(s). Since the closest packed (111) layers of atoms of the
FCC elements |
interpenetrate each other, their crystals do not have distinct cleavage
planes. |
. |
Crystal habit |
The habit of a crystal is its propensity to assume a characteristic outward
shape |
as
it grows. As mentioned previously, this depends on its internal
lattice structure |
as
well as the particular chemical and physical factors present in the
immediate |
environment of the growing crystal. As a result the crystals of most
elements and |
minerals have several common habits. The characteristic crystal
habit(s) of a group |
of
structurally similar elements or minerals is usually represented by a member
of |
group that best displays its properties. For the FCC elements this is
gold. |
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 |
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not shown |
Ex.
Au |
dodecahedral |
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cubic |
octahedral |
twinned |
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Figure 46 - Crystal habits of FCC elements |
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Knowhere |
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32 - Structure matters - FCC elements |
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