A new X-ray investigation of maximum microcline crystalline solutions

Refined unit-cell dimensions and molar volumes of a mircocline-low albite ion-exchange series previously studied by Waldbaum and Robie (1971) have been redetermined. Members in the sodic half of the series were found to have significantly larger b dimensions than those previously reported, resolving the major difference between the above study and that of Orville (1967). W _v, the Margules parameter related to the volume of mixing, is significantly lower (0.078 cal/bar mol) than those determined in either of the investigations above. However, it is close to values of W _v determined for several alkali feldspar series with topochemically monoclinic Al-Si distributions. Thus, the dependence of K-Na volume of mixing properties on Al-Si distribution in alkali feldspars is doubtful.