LAUSR

We report thenewmineralhydroxykenoelsmoreite,whichhas beenapprovedbytheIMAasIMA2016-056.Themineraloccurs at the Masaka gold mine, Burundi, as rosettes up to 150mm across of platy crystals up to 20μm wide but <2μm thick, associated with goethite and galena. Crystals are canary yellow, transparent with a vitreous lustre, and have a pale yellow streak. Hydroxykenoelsmoreite is uniaxial (-) and non-pleochroic. The refractive indices were too high to measure, but the Gladstone-Dale compatibility index predicts n = 2.065. Crystals are brittle with an irregular fracture, but have perfect cleavage on {0 0 1}. TheMohs hardness is ∼3 by analogy with hydrokenoelsmoreite. The mineral is a member of the elsmoreite group of the pyrochlore supergroup, but deviates from the ideal cubic symmetry due mainly to ordering of Fe onto one of two W sites. Its structure is trigonal, space group R3, with unit-cell parameters a = 7.313(2), c = 17.863(7) A, V = 827(1)A3 and Z = 6. The empirical formula (based on 7 (O+OH) per formula unit (pfu)) is: (□PbCa NaKBa)(W Fe Al)(O(OH))(OH). Raman spectroscopy and bond- valence sums showed that molecular HO was absent or nearly so. The calculated density is 5.806 g cm.