Physical Aspects of Exsolution in Natural Alkali Feldspars

摘要: At high temperatures alkali feldspars form a complete series of solid solutions with monoclinic symmetry between albite and K-feldspar. On cooling, different intracrystalline processes may occur we consider that the evolution perthitic textures is determined by minimizing strain energy. It possible to calculate energies involved in these processes: a) diffusive segregation potassium sodium atoms giving exsolution K-rich Na-rich lamellae either spinodal decomposition or homogeneous heterogeneous nucleation; b) symmetry change from C2/m C l twinning due reversible displacement silicon tetrahedra sodium-rich feldspars, and/or an ordering aluminum framework lamella. The instantaneous, whereas Al/Si ordering, diffusive process, geologically slow.