Low temperature alkali feldspar series

Mixtures of microcline and low albite containing different proportions of the two feldspars have been heated at 1025° C and the shift of d201 lines has been used to evaluate the extent of homogenisation. It has been assumed that during the short period of heating (96 hours) no appreciable disorder of Al-Si sets in, and with this assumption, a tentative subsolidus diagram for the microcline - low albite system has been proposed.

Natural orthoclase perthites have been heated at 1025° C for different intervals of time and the extent of homogenisation has been studied as a function of time using 131 doublet separation value as an index. It has been found that no homogenisation takes place for the first two hours, after which rate of homogenisation becomes rapid, and after 8 hours the homogenisation is practically complete.