MINERALS AND SYNTHETIC COMPOUNDS, AmXn, WITH CLOSE PACKED

X ATOMS AND A ATOMS OCCUPYING TRIGONAL PRISMATIC INTERSTICES

 
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Molybdenite

                  click here to see a key to this data bar                                  

trigonal prism

50%

hp

layer

3 edges

A- 6c, X- 3c/hp

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  structure

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. .
     The molybdenite layer structure is similar to the gibbsite layer structure seen .
before.  However in molybdenite the occupied layers are HP and alternate with .
unoccupied layers that are packed CCP.   The A atoms reside in 50% of the trigonal
prismatic interstices of the occupied layer.
. .
Ex. MoS2  ( molybdenum sulfide, molybdenite )   ( Mo - A , S - X ) .
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Crystal lattice
     The lattice model shows the occupied HP layers alternating with the unoccupied
CCP layers.  The intervening CCP layer staggers the occupied layers relative to each
other so that the vertical sequence of the X atoms is AABBAA... 
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molybdenite.gif

 
    Figure 117 -  Molybdenite lattice

click image to enlarge

                            structure
   
 
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Polyhedral framework
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linking surfaces

molybdenite.gif

 

   Figure 118 -  Molybdenite polyhedral
                 framework model
             ( 17 T, 20 S,  53 pinges )

3 edges

                        click image to enlarge
.      
     The polyhedral framework model demonstrates the AABB sequence of the X
atoms, the staggering of the occupied AX6 groups in alternating layers, and their
edge linkage. (the black triangles are braces)
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