EQUIATOMIC MINERALS OF EXTENSIVE COMPOSITIONAL SERIES

Abstract

In the present paper we emphasize that only the techniques of statistical mineralogy have been able to establish that the relatively high frequency of equiatomic minerals with end-member ratios between approximately 40:60 and 60:40 in binary series is a rather pronounced geological tendency. For example, in the andradite-grossular series, the central chemical variety is aplome in the ferrispinels it is magnomagnetite; in the ditrigonal scalenohedral carbonates, spherosiderite; and in the eightfold-hydrated arsenates, nickel erythrite. The greatest energy effect and, as a consequence, relatively high stability of the crystal lattice of a mineral, is achieved in the equiatomic region. The statistical data and theoretical reasoning also indicate that equiatomic minerals will have comparatively high stability. This discussion is of considerable interest for many areas of mineralogy (typomorphism, distinguishing between chemical varieties and the like).