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.
.      
 

lawrencite.gif

 
    Figure 79 -  FeCl2 lattice structure

click image to enlarge

                     
   
 
.      
Polyhedral framework
.      

linking surfaces

lawrencite.gif

 

   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
.

Back to mineral table

Back to Knowhere

Home page

page 52 of lesson

Page  53 - Structure matters - CdCl2

page 54 of lesson

 

home   sitemap   products   Polywood   .networks   contact us   Knowhere   3Doodlings