ALBERT

Description: 〈div data-abstract-type="normal"〉 〈p〉This study presents a complete characterization of kenoplumbomicrolite, (Pb,□)〈span〉2〈/span〉Ta〈span〉2〈/span〉O〈span〉6〈/span〉[□,(OH),O], occurring in an amazonite pegmatite from Ploskaya Mountain, Western Keivy Massif, Kola Peninsula, Murmanskaja Oblast, Northern Region, Russia.〈/p〉 〈p〉Kenoplumbomicrolite occurs in yellowish brown octahedral, cuboctahedral and massive crystals, up to 20 cm, has a white streak, a greasy lustre and is translucent. The Mohs hardness is ~6. Attempts to measure density (7.310–7.832 g/cm〈span〉3〈/span〉) were affected by the ubiquitous presence of uraninite inclusions. Reflectance values were measured in air and immersed in oil. Kenoplumbocrolite is optically isotropic. The empirical formula is (Pb〈span〉1.30〈/span〉□〈span〉0.30〈/span〉Ca〈span〉0.29〈/span〉Na〈span〉0.08〈/span〉U〈span〉0.03〈/span〉)〈span〉Σ2.00〈/span〉(Ta〈span〉0.82〈/span〉Nb〈span〉0.62〈/span〉Si〈span〉0.23〈/span〉Sn〈span〉4+〈/span〉〈span〉0.15〈/span〉Ti〈span〉0.07〈/span〉Fe〈span〉3+〈/span〉〈span〉0.10〈/span〉Al〈span〉0.01〈/span〉)〈span〉Σ2.00〈/span〉O〈span〉6〈/span〉[□〈span〉0.52〈/span〉(OH)〈span〉0.25〈/span〉O〈span〉0.23〈/span〉]〈span〉Σ1.00〈/span〉 (from the crystal used for the structural study) and (Pb〈span〉1.33〈/span〉□〈span〉0.66〈/span〉Mn〈span〉0.01〈/span〉)〈span〉Σ2.00〈/span〉(Ta〈span〉0.87〈/span〉Nb〈span〉0.72〈/span〉Sn〈span〉4+〈/span〉〈span〉0.18〈/span〉Fe〈span〉3+〈/span〉〈span〉0.11〈/span〉W〈span〉0.08〈/span〉Ti〈span〉0.04〈/span〉)〈span〉Σ2.00〈/span〉O〈span〉6〈/span〉[□〈span〉0.80〈/span〉(OH)〈span〉0.10〈/span〉O〈span〉0.10〈/span〉]〈span〉Σ1.00〈/span〉 (average including additional fragments). The mineral is cubic, space group 〈span〉Fd〈/span〉〈span〉〈span〉〈img data-mimesubtype="gif" data-type="simple" src="http://static.cambridge.org/resource/id/urn:cambridge.org:id:binary:20181109112359083-0385:S0026461X18000075:S0026461X18000075_inline1.gif"〉 〈span data-mathjax-type="texmath"〉 〈/span〉 〈/span〉〈/span〉〈span〉m〈/span〉. The unit-cell parameters refined from powder X-ray diffraction data are 〈span〉a〈/span〉 = 10.575(2) Å and 〈span〉V〈/span〉 = 1182.6(8) Å〈span〉3〈/span〉, which are in accord with those obtained previously from a single crystal of 〈span〉a〈/span〉 = 10.571(1) Å, 〈span〉V〈/span〉 = 1181.3(2) Å〈span〉3〈/span〉 and 〈span〉Z〈/span〉 = 8. The mineral description and its name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA2015-007a).〈/p〉 〈/div〉