The discreditation of oboyerite and a note on the crystal structure of plumbotellurite

Abstract

The mineral ‘oboyerite’, first described in 1979 from the Grand Central mine, Tombstone, Cochise County, Arizona, USA, has been re-examined. The type specimen from the Natural History Museum, London and a specimen from the Natural History Museum of Los Angeles County (traceable to S. A Williams, who first described ‘oboyerite’) were analysed in this study. The discreditation of ‘oboyerite’ as a valid mineral species has been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (Proposal 19-D). Single-crystal X-ray diffraction, powder X-ray diffraction, electron probe microanalysis and scanning electron microscopy were all employed to show that ‘oboyerite’ is formed of at least two distinct phases, including the lead–tellurium oxysalt minerals ottoite and plumbotellurite. During the course of the discreditation, plumbotellurite was confirmed to be identical to the synthetic compound α-Pb2+Te4+O3. Previously, in some mineralogical literature plumbotellurite was described as orthorhombic with no known crystal structure.

Elucidating the natural–synthetic mismatch of Pb2+Te4+O3: The redefinition of fairbankite to Pb122+(Te4+O3)11(SO4)

“…The combined studies of plumbotellurite (Missen et al 2019) and fairbankite unequivocally align our understanding of the synthetic Pb 2+ Te 4+ O 3 materials with occurrences in Nature. Until these studies, the complexity of natural mineralogical phases has led material scientists, crystallographers, geologists and mineralogists 'up the garden path', believing that there might be 5 or 6 different polymorphs of what is stoichiometrically a simple chemical composition.…”

“…Since Williams had also supplied other major museums with fairbankite "type" material (although he does not state any depository in his 1979 paper), we reinvestigated the fairbankite specimen in the collection of the National Museum of Natural History (Smithsonian), Washington, USA. Similar issues with official and nonofficial "type" material were experienced in the study of 'oboyerite' (Missen et al 2019).…”

“…Minerals whose definitions are based on wet chemistry or other bulk techniques must be reinvestigated de rigueur. The most recent decades in mineralogical research have resulted in a greater appreciation in how micro-and even nanoscale intergrowths of minerals inform macro-scale properties of mineral assemblages, an approach which relies upon accurate characterization of rare phases (Kampf et al, 2017;Missen et al, 2019). In many cases secondary (Te) minerals remain poorly characterized (Christy et al, 2016a), despite the tendency for these minerals to have unique structures which have never been synthesized.…”

“…1-3) also doubles as the former type specimen of 'oboyerite' (Williams, 1979), which is now designated as a 'dead type' for that mineral (Missen et al, 2019). The specimen contains fairbankite and winstanleyite, with the winstanleyite on the specimen misidentified as 'oboyerite' (Williams, 1979;Missen et al 2019). Fairbankite was considered dubious on the sample for many years, as sampling from this type specimen had yielded only cerussite, or occasionally anglesite.…”

“…Data for the discredited (Burke, 2006) lead tellurite mineral 'dunhamite' (Fairbanks, 1946) is entirely lacking. Recently, Missen et al (2019) demonstrated that plumbotellurite (Back, 1990) was incorrectly characterized and is in fact the natural analogue of synthetic α-Pb 2+ Te 4+ O 3 (Zavodnik et al, 2008), leaving only fairbankite as a mismatch with the two remaining synthetic compounds. Fairbankite was originally reportedwithout a crystal structure and on the basis of a wet-chemical analysisas triclinic Pb 2+ Te 4+ O 3 by Williams (1979) from the Tombstone mining area, Arizona, USA.…”