The origin of the phase distribution in two pathetic alkali feldspars

Publisher Website
Google Scholar
Abstract
Ion-thinned foils of two perthites of compositions 57·3 and 53·7 wt. % KAISi3O8 have been examined in the electron microscope at 100 and 1000 kV with the object of quantifying and determining the origin of the distribution of phases. The results indicate that the microstructure is consistent with initial phase separation by spinodal decomposition on (601) followed by coarsening. The initial planar distribution of phases is replaced by discrete particles of Na-rich feldspar in a K-rich matrix; rafting of the Na-rich particles during the later stages of coarsening results, in particle alignment. It is shown that the scale of the micro structural features can be related to the cooling rate of the parent rock.