SHORT COMMUNICATIONS Minerals of rhenium

R]-IEI~IUM is an extremely rare element and a magnitude of c. 5 X 10-4 ppm for its abundance in igneous rocks has been assessed recently (Morris aud Short, 1965). I t may be classed as a dispersed element in the sense of Vernadsky (1924), i.e. it occurs primarily in minerals of other elements. Only in recent years has evidence appeared for the existence of minerals with rhenium as a major constituent and, as most of the details have been published in languages other than English, it is felt that a brief report may be of interest. Rhenium shows a close geochemical coherence with molybdenum and is found in molybdenites of various genetic types in amounts varying from traces up to the value of 1.88 ~ found in deposits in Armenia SSR (Magak'yan et al., 1963). This is not unexpected, since the ionic radii of Re 4+ (0.74.~) and Mo 4+ (0"70.~) are alike and ReS 2 and MoS2 have similar crystal structures and dimensions (Jellinek, 1963). However, although it has been shown that rhenium is carried by molybdenit