Non-equilibrium mixing in natural alkali feldspars

Chemical-optical and X-ray analysis of some perthite groups, from cristalline rock massifs, came into evidence that in perthites with the same order degree of Si/Al distribution, the observed variations of 2V_X are strictly related to the Na content in the potassic phase; i.e. 2V_X decreases when Ab mixed in the K-phase increases.This fact suggests that for any Si/Al, distribution, not in equilibrium, exists a certain range of non equilibrium mixing between Or and Ab.