Abstract
In a recent note, Phillips and Ransom (1968) state that in some gneisses from Broken Hill, New South Wales, there is a correlation between measured volume percentages of quartz in myrmekite and those predicted by Schwantke's (1909) exsolution hypothesis. It is, however, surprising that Phillips and Ransom do not discuss the errors involved in arriving at their results since the difficulties in measuring the volume of vermicular bodies of quartz in plagioclase are great. Even the coarse vermicules from Broken Hill have a diameter of only the thickness of a normal thin section and a simple measurement of two dimensional area will not represent three-dimensional volume. The best measurements would be obtained from myrmekites in which the quartz vermicules are seen in cross section, but this situation is rarely, if ever, attained over large areas and involves an additional error when the vermicules are differentially concentrated in radiating bundles.
