Crystal Chemistry of the Plagionite Group

Abstract

LEAD forms a large number of complex sulphosalts. At least twelve Pb–As and nineteen Pb–Sb sulphosalt minerals are known¹ and, although the Pb–As minerals have received considerable study, no structure for a Pb–Sb sulphosalt has been completely determined. Curiously, minerals in the two systems exhibit little similarity in either composition or lattice constants in spite of the fact that isomorphism and even complete solid solubility are found for a number of arseno- and antimonian sulphosalts. This is undoubtedly due to the rather different sizes of As and Sb coordination groups relative to the dimensions of a Pb–S polyhedron.