Abstract :
A two-dimensional model of Al, Si ordering in alkali feldspar is formulated and used to calculate accurately 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 axact 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 obitained by using approximate calculations for the same model.
