• journal_title：Mineralogical Magazine
• Contributor：A. R. Kampf ; S. J. Mills ; B. P. Nash ; R. M. Housley ; G. R. Rossman ; M. Dini
• Publisher：Mineralogical Society of Great Britain and Ireland
• Date：2013-06-01
• Format：text/html
• Language：en
• Identifier：10.1180/minmag.2013.077.4.05
• journal_abbrev：Mineralogical Magazine
• issn：0026-461X
• volume：77
• issue：4
• firstpage：453
• section：Articles

Camaronesite (IMA 2012-094), [Fe³⁺(H₂O)₂(PO₃OH)]₂(SO₄)·1–2H₂O, is a new mineral from near the village of Cuya in the Camarones Valley, Arica Province, Chile. The mineral is a low-temperature, secondary mineral occurring in a sulfate assemblage with anhydrite, botryogen, chalcanthite, copiapite, halotrichite, hexahydrite, hydroniumjarosite, pyrite, römerite, rozenite and szomolnokite. Lavender-coloured crystals up to several mm across form dense intergrowths. More rarely crystals occur as drusy aggregates of tablets up to 0.5 mm in diameter and 0.02 mm thick. Tablets are flattened on {001} and exhibit the forms {001}, {104}, {015} and {018}. The mineral is transparent with white streak and vitreous lustre. The Mohs hardness is 2½, the tenacity is brittle and the fracture is irregular, conchoidal and stepped. Camaronesite has one perfect cleavage on {001}. The measured and calculated densities are 2.43(1) and 2.383 g/cm³, respectively. The mineral is optically uniaxial (+) with ω = 1.612(1) and ε = 1.621(1) (white light). The pleochroism is O (pale lavender) > E (colourless). Electron-microprobe analyses provided Fe₂O₃ 31.84, P₂O₅ 29.22, SO₃ 15.74, H₂O 23.94 (based on O analyses), total 100.74 wt.%. The empirical formula (based on 2 P a.p.f.u.) is: Fe_1.94(PO₃OH)₂(S_0.96O₄)(H₂O)₄·1.46H₂O. The mineral is slowly soluble in concentrated HCl and extremely slowly soluble in concentrated H₂SO₄. Camaronesite is trigonal, R32, with cell parameters: a = 9.0833(5), c = 42.944(3) Å, V = 3068.5(3) ų and Z = 9. The eight strongest lines in the X-ray powder diffraction pattern are [d_obs Å(I)(hkl)]: 7.74(45)(101), 7.415(100)(012), 4.545(72)(110), 4.426(26)(018), 3.862(32)(021,202,116), 3.298(93)(027,119), 3.179(25)(208) and 2.818(25)(1·1·12,125). In the structure of camaronesite (R₁ = 2.28% for 1138 F_o > 4σF), three types of Fe octahedra are linked by corner sharing with (PO₃OH) tetrahedra to form polyhedral layers perpendicular to c with composition [Fe³⁺(H₂O)₂(PO₃OH)]. Two such layers are joined through SO₄ tetrahedra (in two half-occupied orientations) to form thick slabs of composition [Fe³⁺(H₂O)₂(PO₃OH)]₂(SO₄). Between the slabs are partially occupied H₂O groups. The only linkages between the slabs are hydrogen bonds. The most distinctive component in the structure consists of two Fe octahedra linked to one another by three PO₄ tetrahedra yielding an [Fe₂(PO₄)₃] unit. This unit is also the key component in the sodium super-ionic conductor (NASICON) structure and has been referred to as the lantern unit. The polyhedral layers in the structure of camaronesite are similar to those in the structure of taranakite. The Raman spectrum exhibits peaks consistent with sulfate, phosphate, water and OH groups.