CALCIUM MOTTRAMITE, THE FIRST KNOWN REPRESENTATIVE OF A NEW ISOMORPHIC MOTTRAMITE-TANGEITE SERIES

Abstract

The authors found mottramite, a rare lead vanadate and an end member in the mottramite-descloizite series together with pyromorphite in the outer contact zone of the Murun pluton in Yakutia. It was enclosed in a peculiar and uncommon rock known as torgolite. A detailed study of the chemical composition of this mottramite indicates that, in addition to grains in which the content of PbO exceeds 50 percent (making such grains equivalent in terms of composition to classic mottramite, there are grains with a PbO content as low as 39 percent. There may also exist grains with a still lower PbO content. Grains low in PbO generally contain from 21 to 24 percent CuO, much more than reported before for even pure mottramite. These grains, also contain CaO, which has not been found in mottramite in any previous studies, whereas such a characteristic component of this group of minerals as ZnO is found only in occasional grains and then only in quantities not exceeding 1 percent.