Abstract
A two-dimensional model of Al, Si ordering in alkali feldspar is formulated
and used to calcul~tea ccurately the configurational entropy for the model. For
this purpose, a new method called Independent Basic Unit or IBU is introduced.
To compare the results with the exact values, this method is applied to the onedimensional
model of albite. The results given by IBU are found to be accurate
to the extent that the deviation in free energy is less than 0.8%. The reduced
configurational entropy is calculated to 'be 1.065 corresponding to 8.854 J K-1
mol-1 for the two-dimensional model. This value is within 6% of standard
values obtained by using approximate calculations for the same model
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