|
|
MINERALS AND SYNTHETIC COMPOUNDS, AmXn, IN WHICH X
ATOMS ARE |
|
CLOSE PACKED AND A ATOMS OCCUPY OCTAHEDRAL INTERSTICES |
| |
|
. |
|
CdCl2 |
|
click here to see a key to this data bar
|
|
octa |
50% |
fcc |
layer |
6
edges |
A-
6c, X- 3c/fcc |
|
. |
|
structure |
. |
|
. |
. |
|
CdCl2 is a
layered structure in which 100% of the octahedral voids of alternate |
. |
|
layers of FCC close
packed X atoms are occupied with A atoms resulting in a 50% |
. |
|
rate overall. |
| |
. |
|
Ex. FeCl2 ( ferrous chloride,
lawrencite ) ( Fe - A , Cl - X ) |
. |
|
. |
|
Crystal lattice |
|
The layer structure of
the crystal is clearly demonstrated by the FCC lattice if the |
|
layer of occupied AX6 groups is
colored differently than the unoccupied layer. The |
|
layers are oriented parallel to the (111) plane. |
| . |
|
|
|
| |
|
|
|
Figure 79 - FeCl2 lattice structure |
|
click image to enlarge |
|
| |
|
| |
| . |
|
|
|
|
|
Polyhedral framework |
| . |
|
|
|
|
linking surfaces |
|
|
|
|
Figure 80 -
FeCl2 polyhedral |
|
framework model |
|
( 84T, 110 pinges) |
|
6
edges |
click image to enlarge |
| . |
|
|
|
|
|
The polyhedral
framework model demonstrates that the AX6 coordination groups |
|
are linked by their perimeter edges to form the
occupied layers. The black triangles |
|
simply brace the structure to separate the
layers and orient them properly. |
|
. |
|
Cleavage |
Crystal habit |
|
(0001) |
hexagonal tablet |
|
. |
|
|
|
Isostructural minerals/compounds |
|
CdCl2, MgCl2, CoCl2,
NiCl2, NbS2, TaS2, CdBr2, NiI2 |
|
. |
|
|
 |
Page
53 - Structure matters - CdCl2 |
 |