|
Cleavage |
. |
(111) - perfect - parallel to the (111) close packed layers |
. |
|
. |
Crystal habit |
. |
Predominately octahedral, less commonly dodecahedral, rarely
cubic, |
. |
occasionally tetrahedral; twinning on (111) very common. |
. |
. |
|
|
|
 |
 |
Figure 55 - Crystal habits |
of
diamond structure |
elements
|
|
. |
tetrahedral |
rhombicuboctahedral |
. |
|
|
|
. |
The graphite and diamond polymorphs of carbon is a classic illustration of
the |
. |
effect that the geometry of the atomic packing has on the chemical and
physical |
properties of matter. In its graphite form carbon is one of the
softest natural |
materials known and it is a good lubricant. In contrast, in its
diamond form, it is the |
hardest natural material known and it is an excellent abrasive. The
tetrahedral |
arrangement of the carbon atoms in diamond is primarily responsible for its |
hardness due to the omni-triangulated nature of its structure.
Carbon's extreme |
polymorphism is the result of the different conditions under which its
crystals are |
formed. It is only when carbon is subjected to extremes of temperature
and pressure |
that it morphs into the diamond structure. |
. |
Only a few native elements exist in pure form in their natural state on
earth (Au, |
Ag,
Cu, Hg, Pb, Pt, Sn, Fe, C, S, Sb, As, Bi, and the inert gases). The
rest must be |
extracted, refined, and crystallized from their ore minerals. The
following section |
describes the geometry and symmetry of minerals in terms of their topology. |
Back to
Knowhere |
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37 - Structure matters - Diamond structure elements |
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