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

                  click here to see a key to this data bar                                  

octa

100%

hcp

3-d

2 faces, 6 edges

A- 6c, X- 6c/hcp

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  structure

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. .
     The NiAs structure is comprised of HCP packed X atoms with A atoms occupying .
100% of the octahedral interstitial voids in each successive close packed layer. .
  .
Ex. NiAs  ( nickel arsenide, niccolite or nickeline )     ( Ni - A , As - X ) .
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Crystal lattice
     Since all of the octahedral voids are occupied the crystal can be modeled as
a simple HCP lattice with all of the AX6 coordination groups in a layer colored the
same color.  The eclipsed arrangement of these groups in each successive layer
is evident by the lattice.
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niccolite.gif

 
    Figure 75 -  NiAs lattice structure

click image to enlarge

                     
   
 
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Polyhedral framework
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linking surfaces

niccolite.gif

 

   Figure 76 -  NiAs polyhedral
           framework model
           ( 66 T,  81 pinges)

2 faces, 6 edges

                click image to enlarge
.      
     The polyhedral framework demonstrates that the AX6 octahedral coordination
groups stack together in the HCP configuration so that each shares two faces and
six edges with adjacent groups.  Compare this structure with halite which is FCC.
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Cleavage

Crystal habit

     none      pyramidal (rare)
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Isostructural minerals/compounds
AuSn, CoS, CoSb, CoSe, CoTe, CrSb, CrSe, CrTe, CuSn, FeS, FeSb, FeSe, FeTe,
IrSb, IrTe, MnAs, MnBi, MnSb, MnTe, NiSb, NiSe, NiTe, PdSb, PdTe, PtB, PtSb, PtSn,
RhBi, RhTe, ScTe, TiS, TiSe, TiTe, VP, VS, VSe, ZrTe
.

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