Recent investigations have revealed a family of very simply-built oxyhalides, containing bismuth together with another metal. These, compounds all form tetragonal plates; metal-oxygen sheets, which have in all substances the same construction, extend parallel to the largest faces. The ilíe-0-sheets are separated by halogen sheets, which may be single (^-compounds), double (X 2 ) or triple (X3). The tetragonal α-axis is always close to 3.9 Á, which is easily explained from the structure of the Me- Olayers (Sillén, 1940).We thought it of interest to search for the same simple construction principles in oxyhalides containing no bismuth. As first objects of study we chose the minerals nadorite, PbSb0 2 Cl, and ekdemite, a lead-arsenic oxychloride for which several different formulae have been proposed. The crystal structure of nadorite was worked out, and proved to be, in principle, an X 1 structure, where however the two sorts of metal atoms are ordered in rows, whereby the symmetry descends to orthorhombic. It could be shown that the mineral named ochrolite is identical with nadorite.Our work on ekdemite is also recorded. Here the conditions are more complex, and no certain conclusions could be drawn.
Syntheses in the system PbSbOCl. TetragonalPbSb02Cl.Lead chloride was fused together with Sb 2 0 3 , mixtures of PbO and Sb 2 0 3 in various proportions, or PbO. Series of samples were prepared in porcelain crucibles and in evacuated tubes of Supremax glass; in both cases one series with rapid and one with slow cooling of the melts was made. The cooled product was ground and, for removal of the surplus of PbCl 2 , brought into a large beaker with cool water. After 5-10 hours of electric stirring the insoluble residue was filtered off and dried in a cool vacuum desiccator. The powder photographs revealed in these samples 1) a tetragonal phase, 2) nadorite, which is orthorhombic, 3) a phase which was obtained pure when PbO was added to PbCl 2 and which consequently contains no antimony. It seems improbable that the two first phases should contain antimony of higher valency than three, as they were obtained also
