Polymorf - Knowhwere- FCC elements

Polyhedral framework

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.

Cleavage

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.


				not shown
Ex. Au				dodecahedral


	cubic	octahedral	twinned

Figure 46 - Crystal habits of FCC elements
.
Back to Knowhere

Page 32 - Structure matters - FCC elements