MINERALS AND SYNTHETIC COMPOUNDS, AmXn, IN WHICH X ATOMS ARE
          CLOSE PACKED AND A ATOMS OCCUPY TETRAHEDRAL INTERSTICES
 
.
Antifluorite

                  click here to see a key to this data bar                                  

tetra

100%

fcc

3-d

6 edges

A- 4c, X- 8c/fcc

.
  structure .
. .
     In the antifluorite structure the X atoms are packed in the FCC arrangement and .
the A atoms occupy 100% of the tetrahedral interstices. .
  .
Ex. Ag2S ( aluminum sulfide, argentite ) - high temperature form    ( Ag - A , S - X ) .
.
Crystal lattice
     The lattice can be modeled as a simple FCC packing with the understanding that
100% of the tetrahedral voids formed by the FCC packed sulfur anions are occupied
by silver cations thereby forming AX4 coordination groups of atoms.  It is understood
that none of the octahedral voids are occupied.
.      
 

antifluorite.gif

 
    Figure 58 -  Antifluorite lattice

click image to enlarge

                              structure
   
 
.      
     The above image demonstrates the staggered FCC arrangement of the occupied
tetrahedra.  The layers are numbered in the sequence of their vertical order from
the bottom layer up.  The occupied AX4 groups are colored differently in each layer
to differentiate the layers from one another.
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Polyhedral framework
.      

linking surfaces

antifluorite.gif

 

   Figure 59 -   Antifluorite polyhedral
                   framework model
                  ( 112 T,  112 pinges)

4 edges

                          click image to enlarge
.      
     The polyhedral framework model clearly shows that 100% of the tetrahedrally
coordinated groups of X atoms are occupied with A atoms.  The structure is built up
by linking all the edges of these tetrahedra together.
.
Cleavage

truncated_cube.gif

 
     (100), (110) - poor   8 LT, 24 RT, 30 SS
           118 pinges
Crystal habit  
     cubic, octahedral, dodecahedral

truncated cube

 
.  
Isostructural minerals/compounds
Na2O, K20, Rb2O, Li2S
.

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