ALBERT

Description: 〈div data-abstract-type="normal"〉〈p〉The new mineral ammoniomathesiusite (NH〈span〉4〈/span〉)〈span〉5〈/span〉(UO〈span〉2〈/span〉)〈span〉4〈/span〉(SO〈span〉4〈/span〉)〈span〉4〈/span〉(VO〈span〉5〈/span〉)·4H〈span〉2〈/span〉O, was found in the Burro mine, San Miguel County, Utah, USA, where it occurs as a secondary phase on asphaltum/quartz matrix in association with ammoniozippeite, gypsum, jarosite and natrozippeite. The mineral forms pale yellow to greenish-yellow prisms, up to ~0.3 mm long, with pale-yellow streak and bright yellow–green fluorescence. Crystals are transparent and have vitreous lustre. The mineral is brittle, with Mohs hardness of 2½, stepped fracture and two cleavages: excellent on {110} and good on {001}. The calculated density is 3.672 g/cm〈span〉3〈/span〉. Ammoniomathesiusite is optically uniaxial (–) with ω = 1.653(2) and ε = 1.609(2) (white light). Pleochroism is: 〈span〉O〈/span〉 = green-yellow, 〈span〉E〈/span〉 = colourless; 〈span〉O〈/span〉 〉 〈span〉E〈/span〉. Electron microprobe analyses yielded the empirical formula [(NH〈span〉4〈/span〉)〈span〉4.75〈/span〉(UO〈span〉2〈/span〉)〈span〉4〈/span〉(SO〈span〉4〈/span〉)〈span〉4〈/span〉(VO〈span〉5〈/span〉)·4(H〈span〉2.07〈/span〉O). The five strongest powder X-ray diffraction lines are [〈span〉d〈/span〉〈span〉obs〈/span〉 Å(〈span〉I〈/span〉)(〈span〉hkl〈/span〉)]: 10.57(46)(110), 7.10(62)(001), 6.41(100)(101), 3.340(35)(240) and 3.226(44)(141). Ammoniomathesiusite is tetragonal, 〈span〉P〈/span〉4/〈span〉n〈/span〉 with 〈span〉a〈/span〉 = 14.9405(9), 〈span〉c〈/span〉 = 7.1020(5) Å, 〈span〉V〈/span〉 = 1585.3(2) Å〈span〉3〈/span〉 and 〈span〉Z〈/span〉 = 2. The structure of ammoniomathesiusite (〈span〉R〈/span〉〈span〉1〈/span〉 = 0.0218 for 3427 〈span〉I〈/span〉 〉 2σ〈span〉I〈/span〉) contains heteropolyhedral sheets based on [(UO〈span〉2〈/span〉)〈span〉4〈/span〉(SO〈span〉4〈/span〉)〈span〉4〈/span〉(VO〈span〉5〈/span〉)]〈span〉5–〈/span〉 clusters. The structure is identical to that of mathesiusite, with 〈span〉〈span〉〈img data-mimesubtype="gif" data-type="simple" src="http://static.cambridge.org/resource/id/urn:cambridge.org:id:binary:20190313104343836-0311:S0026461X18001123:S0026461X18001123_inline1.gif"〉 〈span data-mathjax-type="texmath"〉 〈/span〉 〈/span〉〈/span〉 in place of K〈span〉+〈/span〉.〈/p〉〈/div〉