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

                  click here to see a key to this data bar                                  

octa

1/3

ABBAA

layer

3 edges

A- 6c, X- 2c/ABBAA

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 structure

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. .
     Gibbsite is a naturally occurring polymorph of bayerite which is identical in .
structure except that the alternating occupied close packed layers stack together in .
the HP (simple hexagon) sequence.  Therefore the sequencing is ABBAABB...
  .
Ex. Al(OH)3  ( aluminum hydroxide, gibbsite )   ( Al - A , OH - X ) .
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Crystal lattice
     The HP layering sequence of the hexagonal nets of AX6 coordination groups of
atoms is clearly demonstrated by the lattice model.  The 2/3 occupancy rate of the
octahedral voids of these occupied layers can also be extracted from the model.
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gibbsite.gif

 
    Figure 94 -  Gibbsite lattice structure

click image to enlarge

                       
   
 
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Polyhedral framework
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linking surfaces

gibbsite.gif

 

        Figure 95 -   Gibbsite polyhedral
                   framework model
               ( 72 T, 3 S, 132 pinges )

3 edges

                          click image to enlarge
.      
     The polyhedral framework model demonstrates the HP sequence of the hexagonal
rings of the occupied layers ( black squares are braces to separate and properly orient
the layers).
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Cleavage

Crystal habit

     (100) - perfect      hexagonal tabular
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