Summary of minerals with AX4 coordination group structures .
     The number and type of linkage surfaces of close packed AX4 coordination groups .
comprising the forgoing crystal structures depended on the percent occupation of the .
structure's tetrahedral voids with A atoms, the type of packing of the X atoms, and .
whether the occupied layers of the lattice were successive or alternating.  The range
of linkage varied from AX4 groups that shared all six possible edges to groups that .
shared no surfaces at all.  Throughout this progression these AX4 groups have .
supplied all of the close packed atoms necessary to build the lattice structure. .
     The chemical composition of the crystal also depended on the percent occupation
of the tetrahedral voids.  A close examination of the lattice structures demonstrates
that the ratio of tetrahedral interstices to close packed X atoms in a FCC or HCP
crystal structure is 2:1.  This enables the chemical formula of the mineral to be
deduced a priori from a knowledge of the occupation rate.  This clearly establishes
the structural basis for the chemical composition of these minerals.






% occupation




















1/6 (16.7%)




1/8 (12.5%)




Table 6 -  Percent occupation versus formula for AX4 mineral structures

     The following section illustrates the effect that the percent occupation of the
octahedral voids of crystal lattice structures has on the geometry and chemical
composition of minerals.

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