- journal_title：Mineralogical Magazine
- Contributor：S. J. Mills ; A. R. Kampf ; P. A. Williams ; P. Leverett ; G. Poirier ; M. Raudsepp ; C. A. Francis
- Publisher：Mineralogical Society of Great Britain and Ireland
- Date：2010-
- Format：text/html
- Language：en
- Identifier：10.1180/minmag.2010.074.5.863
- journal_abbrev：Mineralogical Magazine
- issn：0026-461X
- volume：74
- issue：5
- firstpage：863
- section：CNMNC Newsletter 5
id="p-1">Hydroniumpharmacosiderite, ideally (H3O)Fe4Fe4(AsO4)3(OH)4·4H2O, 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 × 0.14 mm × 0.14 mm. The mineral is transparent with a vitreous lustre. It is brittle with a cleavage on {001}, has an irregular fracture, a white streak and a Mohs hardness of 2–3 (determined on H3O-exchanged pharmacosiderite). 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: [(H3O)0.50K0.48Na0.06]1.04(Fe3.79Al0.22)4.01[(As2.73P0.15)2.88O12](OH)4·4H2.14O. The five strongest lines in the X-ray powder diffraction pattern are [dobs(Å),Iobs,(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 Pinline-formula" id="inline-formula-1"><img class="math tex" alt="Formula" src="863/embed/tex-math-1.gif" />3m with a = 7.9587(2) Å, V = 504.11(2) Å3 and Z = 1. The crystal structure was solved by direct methods and refined to R1 = 0.0481 for 520 reflections with I > 2σ(I). The structure is consistent with determinations for H3O-exhchanged pharmacosiderite and the general pharmacosiderite structure type.