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

Halite

                  click here to see a key to this data bar                                  

octa

100%

fcc

3-d

12 edges

A- 6c, X- 6c/fcc

.

  structure

.
. .
     In the halite structure the X atoms are FCC packed and the A atoms occupy all of .
the octahedral interstices in each successive layer.  In the case of the metal halides, .
only the lithium halides and NaI have the proper atomic radius ratios for the halide
atoms to be closest packed.  That is, the X atoms octahedrally coordinated around the
A atoms of the AX6 groups are in contact with each other.  The halite structure is used
by ionic compounds in which the cations and anions have equal but opposite charges
and their ionic radii are significantly different.
  .
Ex. NaCl  ( sodium chloride, halite )      ( Na - A , Cl - X ) .
.
Crystal lattice
     The halite structure can be modeled as a simple FCC lattice.  Since all of the
octahedral voids are occupied, the AX6 groups within each layer can be modeled
with the same color.  It is understood that none of the tetrahedral voids are occupied.
.      
 

halite.gif

 
    Figure 73 -  Halite lattice structure

click image to enlarge

                         
   
 
.      
     The FCC staggered arrangement of the AX6 groups in each successive layer is
evident in the lattice model.
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Polyhedral framework
.      

linking surfaces

halite.gif

 

   Figure 74 -  Halite polyhedral
            framework model
            ( 48 T,  60 pinges)

12 edges

                click image to enlarge
.      
     The polyhedral framework is built up by linking the octahedral AX6 groups
together by their edges.
.
Cleavage

click to enlarge

 
     (100) - perfect  twinning on (111),
.  interpenetrating cube
Crystal habit      click image to enlarge
     cubic (hopper common), octahedral (rare)
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Isostructural minerals/compounds
AgBr, AgCl, AgF, BaO, BaS, BaSe, BaTe, CaO, CaS, CaSe, CaTe, CdO, CoO, CrN, CsF,
CsH, KBr, KCl, KF, KH, KI, LiBr, LiCl, LiF, LiH, LiI, MgO, MgS, MgSe, MnO, MnS, MnSe,
NaBr, NaF, NaH, NaI, NbC, NbO, NiO, PbS, PbSe, PbTe, PdH, RbBr, RbCl, RbF, RbH,
RbI, ScAs, ScN, ScSb, SnAs, SnSb, SnSe, SnTe, SrO, SrS, SrSe, SrTe, TaC, TaO, TiC,
TiN, TiO, VC, VN, YAs, YN, YTe, ZrB, ZrC, ZrN, ZrO, ZrP, ZrS
.

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