Natural and synthetic selenites and selenates and their Gladstone-Dale compatibility
Mandarino, Joseph A.
European Journal of Mineralogy Volume 6 Number 3 (1994), p. 337 - 350
published: Jun 7, 1994
manuscript accepted: Jan 25, 1994
manuscript received: Sep 10, 1992
ArtNo. ESP147050603011, Price: 29.00 €
Abstract The oxysalts of the element selenium, selenites (with Se4+) and selenates (with Se6+) are relatively rare as minerals. Only fifteen selenium oxysalts are known to occur naturally; thirteen are "pure" selenites, i.e., they contain only selenite anionic groups. The other two minerals each contains two anionic groups; in one case, selenate and sulfate, and in the other, selenate and selenite. The selenites are: ahlfeldite, NiSeO3∙2H2O; chalcomenite and clinochalcomenite, CuSeO3∙2H2O; cobaltomenite, CoSeO3∙2H2O; demesmaekerite, Pb2CU5(UO2)2(SeO3)2(OH)6∙2H2O; derriksite, CiH(UO2)(SeO3)2(OH)6; francisite, CU3Bi(SeO3)2O2Cl; guilleminite, Ba(UO2)3(SeO3)2(OH)4∙3H2O; haynesite, (UO2)3(OH)2(SeO3)2∙5H2O; mandarinoite, Fe2(SeO3)3∙6H2O; marthozite, Cu(UO2)3(SeO3)3(OH)2.7H2O; molybdomenite, PbSeO3; and sophiite, Zn2(SeO3)Ch. The selenates are: olsacherite, Pb2(SeO4)(SO4) and schmiederite, Pb2CU2(OH)4(SeO4)(SeO3). In addition, the poorly described "kerstenite" is mentioned in many references and may be PbSeO4, another selenate. The Gladstone-Dale equations were applied to the selenites and selenates to determine the compatibility of the optical data, calculated densities and chemical compositions. Calculations could not be carried out for francisite because optical data are not available, but the distribution among the compatibility categories of the other selenium oxysalts is: superior 7, excellent 4, good 2, fair 0 and poor 1. The compatibility distribution for five synthetic selenates is: superior 2, excellent 2, good 0, fair 1 and poor 0. The data for the only synthetic selenite fell into the superior category. On the basis of the compatibility results, a restudy of marthozite is recommended. In addition, the minimally described "kerstenite" should be properly characterized.