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

Wurtzite

                  click here to see a key to this data bar                                  

tetra

50%

hcp

3-d

4 vertices

A- 4c, X- 4c/hcp

.

  structure

.
. .
     In the wurtzite structure A atoms occupy fifty percent of the interstitial voids of .
HCP packed X atoms.  Wurtzite is the high temperature polymorph of the FCC .
zincblende (sphalerite) structure.
  .
Ex. ZnS ( zinc sulfide, wurtzite ) - high temperature polymorph       ( Zn - A,  S - X ) .
.
Crystal lattice
     The wurzite lattice structure is modeled as a HCP packing of sulfur anions (X). The
occupied AX4 groups are colored differently and pointed in the opposite direction
than tetrahedrally coordinated groups of sulfur atoms whose interstitial voids are
unoccupied (blue).
.      
 

wurtzite.gif

 
    Figure 64 -  Wurtzite lattice structure

click image to enlarge

                       
   
 
.      
     The lattice model clearly shows the eclipsed HCP arrangement of the AX4 groups
in the successive vertical layers as well as the fifty percent occupancy rate. 
.
Polyhedral framework
.      

linking surfaces

wurtzite.jpg

 

   Figure 65 -   Wurtzite polyhedral
                framework model
                ( 59 T,  66 pinges)

4 vertices

                     click image to enlarge
.      
     The vertex linkage of the AX4 tetrahedral coordination groups is clearly evident
in this model.  Compare the HCP wurtzite model with that of the FCC zincblende
polyhedral framework model shown previously.  The following images portray
overhead images of them looking down on the (111) plane.
.    

wurtzite.jpg

zincblende.jpg

 
Figure 66 -  Comparison of
        the wurtzite and
     zincblende structures
 

wurtzite (HCP)

zincblende (FCC)

           click image to enlarge

.    
     Compare the eclipsed arrangement of the AX4 coordination groups in wurtzite and
the staggered arrangement in zincblende.  Recall that the only difference between
the HCP and FCC sphere packings is the positioning of the third, differentiating, layer
of triangulated close packed spheres relative to the first layer.  Only a slight shift in
their relative positions brings about the change in the structure.  Both minerals have
the same chemical composition.  The increased excitation of the atoms caused by
the higher temperatures present when wurtzite crystallizes imparts enough energy to
the system to cause the shift.
 
Crystal habit
     short prismatic to tabular
 
Isostructural minerals/compounds
AgI, AlN, BeO, CdS, CdSe, Cu3AsS4, CuBr, CuCl, CuH, CuI, GaN, InN, MgTe,
MnS, MnSe, MnTe, NbN, TaN, ZnO, ZnSe, ZnTe
.

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