Hydroniumpharmacosiderite, a new member of the pharmacosiderite supergroup from Cornwall, UK: structure and description

作者：Mills S J^*; Kampf A R; Williams P A; Leverett P; Poirier G; Raudsepp M; Francis C A

来源：Mineralogical Magazine, 2010, 74(5): 863-869.

DOI：10.1180/minmag.2010.074.5.863

• hydronium
• pharmacosiderite
• crystal structure
• Cornwall
• new mineral
• hydroniumpharmacosiderite
• UK

Hydroniumpharmacosiderite, ideally (H(3)O)Fe(4)(AsO(4))(3)(OH)(4)center dot 4H(2)O, is a new mineral from Cornwall, UK, probably from the St. Day group of mines. It occurs as a single yellowish green, slightly elongated cube, measuring 0.17 mm x 0.14 mm x 0.14 mm. The mineral is transparent with a vitreous lustre. It is brittle with a cleavage on 1001 has an irregular fracture, a white streak and a Molls hardness of 2-3 (determined on H(3)O-exchanged phamiacosiderite). Hydroniumpharmacosiderite has a calculated density of 2.559 g CM(-3) for the empirical formula. The empirical formula, based upon 20.5 oxygen atoms, is: [(H(3)O)(0.50)K(0.48)Na(0.06)](1.04)(Fe(3.79)Al(0.22))(4.01)[(As(2.73)P(0.15))(2.88)O(12)](OH)(4)center dot 4H(2.14)O. The five strongest lines in the X-ray powder diffraction pattern are [d(obs)(angstrom),I(obs),(hkl)]: 8.050,100,(001); 3.265,35,(112); 2.412,30,(113); 2.830,23,(202); 4.628,22,(111). Hydroniumpharmacosiderite is cubic, space group P (4) over bar 3m with a = 7.9587(2) angstrom, V = 504.11(2) angstrom(3) and Z = 1. The crystal structure was solved by direct methods and refined to R(1) = 0.0481 for 520 reflections with I > 2 sigma(I). The structure is consistent with determinations for H(3)O-exhchanged pharmacosiderite and the general phamtacosiderite structure type.

• 出版日期2010-10