II.—Albitization of Basic Plagioclase Felspars

Since Cathrein in 1883 investigated the nature of saussurite, it has been well known that albite can arise from the alteration of basic plagioclase felspars. He found that the fine-grained aggregate of minerals known as saussurite has commonly been derived from basic felspar, and that the processes involved in the change have led to little more than a chemical re-arrangement within the limits of the original felspar crystal. The bulk composition of the aggregate thus agrees approximately with that of the felspar from which it has been derived, and the albite which separates out is intermingled with lime-bearing silicates such as epidote, zoisite, and garnet.