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La Serena, Chile

Plasil J.,ASCR Institute of Physics Prague | Skoda R.,Masaryk University | Fejfarova K.,ASCR Institute of Physics Prague | Cejka J.,National Museum | And 8 more authors.
Mineralogical Magazine | Year: 2014

The natural hydroniumjarosite sample from Cerros Pintados (Chile) was investigated by electron microprobe, single-crystal X-ray diffraction and vibrational spectroscopy (Infrared and Raman). The chemical composition of studied specimens (wt.%, mean of seven analyses) obtained from electron microprobe (in wt.%): Na2O 1.30, K2O 0.23, CaO 0.04, Fe2O3 50.49, Al2O3 0.37, SiO 2 0.33, SO3 33.88, H2O (calculated on the basis of ∑(OH-+H3O+) deduced from the charge balance) 13.32, total 99.98, corresponds to the empirical formula (H 3O)0.77 +(Na0.20K0.02) S0.22(Fe2.95Al0.03)∑2.98 (OH)6.12[(SO4)1.97(SiO4) 0.03]∑2.00 (calculated on the basis of S + Si = 2 a.p.f.u. (atoms per formula unit)). The studied hydroniumjarosite is trigonal, with space group R3̄m, with a = 7.3408(2), c = 17.0451(6) Å and V = 795.46(4) Å 3. The refined structure architecture is consistent with known jarosite-series minerals, including synthetic hydroniumjarosite. However, in the current study the presence of H3O+ is well documented in difference Fourier maps, where characteristic positive difference Fourier maxima, with apparent trigonal symmetry, were localized in the vicinity of the O4 atom in the channel-voids of the structure. The structure of natural hydroniumjarosite, including the H atoms, was refined to R1 = 0.0166 for 2113 unique observed reflections, with Iobs>3σ(I). The present structure model, which includes the position of the H atom within the hydronium ion, is discussed with regard to the vibration spectroscopy results and earlier published density-functional theory (DFT) calculations for the alunite-like structure containing H3O+. © 2014 The Mineralogical Society. Source


Kampf A.R.,Natural History Museum of Los Angeles County | Mills S.J.,Khan Research Laboratories | Nash B.P.,University of Utah | Housley R.M.,California Institute of Technology | And 2 more authors.
Mineralogical Magazine | Year: 2013

Camaronesite (IMA 2012-094), [Fe3+(H2O) 2(PO3OH)]2(SO4)·1-2H 2O, 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 Fe2O 331.84, P2O529.22, SO315.74, H 2O 23.94 (based on O analyses), total 100.74 wt.%. The empirical formula (based on 2 P a.p.f.u.) is: Fe1.94(PO3OH) 2(S0.96O4)(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) Å3 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 (R 1 = 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 [Fe 3+(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. © 2013 The Mineralogical Society. Source


Kampf A.R.,Natural History Museum of Los Angeles County | Mills S.J.,Khan Research Laboratories | Housley R.M.,California Institute of Technology | Rossman G.R.,California Institute of Technology | And 2 more authors.
Mineralogical Magazine | Year: 2013

Joteite (IMA2012-091), Ca2CuAl[AsO4][AsO 3(OH)]2(OH)2·5H2O, is a new mineral from the Jote mine, Tierra Amarilla, Copiapó Province, Atacama, Chile. The mineral is a late-stage, lowtemperature, secondary mineral occurring with conichalcite, mansfieldite, pharmacoalumite, pharmacosiderite and scorodite in narrow seams and vughs in the oxidized upper portion of a hydrothermal sulfide vein hosted by volcanoclastic rocks. Crystals occur as sky-blue to greenish-blue thin blades, flattened and twinned on {001}, up to ~300 m m in length, and exhibiting the forms {001}, {010}, {110}, {210} and {111}. The blades are commonly intergrown in wheat-sheaf-like bundles, less commonly in sprays, and sometimes aggregated as dense crusts and cavity linings. The mineral is transparent and has a very pale blue streak and vitreous lustre. The Mohs hardness is estimated at 2 to 3, the tenacity is brittle, and the fracture is curved. It has one perfect cleavage on {001}. The calculated density based on the empirical formula is 3.056 g/cm3. It is optically biaxial (-) with α = 1.634(1), β = 1.644(1), γ = 1.651(1) (white light), 2Vmeas = 78(2) and 2Vcalc = 79.4. The mineral exhibits weak dispersion, r < v. The optical orientation is X ≈ c*; Y ≈ b*. The pleochroism is Z (greenish blue) > Y (pale greenish blue) > X (colourless). The normalized electron-microprobe analyses (average of 5) provided: CaO 15.70, CuO 11.22, Al2O38.32, As 2O546.62, H2O 18.14 (structure), total 100 wt.%. The empirical formula (based on 19 O a.p.f.u.) is: Ca 1.98Cu1.00Al1.15As2.87H 14.24O19. The mineral is slowly soluble in cold, concentrated HCl. Joteite is triclinic, P1, with the cell parameters: a = 6.0530(2), b = 10.2329(3), c = 12.9112(4) Å, a = 87.572(2), b = 78.480(2), g = 78.697(2), V = 768.40(4) Å3 and Z = 2. The eight strongest lines in the X-ray powder diffraction pattern are [d obs Å (I)(hkl)]: 12.76(100)(001), 5.009(23)(020), 4.206(26)(120,003,121), 3.92(24)(022,022,102), 3.40(25)(113), 3.233(19)(031,023,123,023), 2.97(132,201) and 2.91(15)(122,113). In the structure of joteite (R 1 = 7.72% for 6003 F o > 4σF), AsO4 and AsO3 (OH) tetrahedra, AlO6 octahedra and Cu2+O5 square pyramids share corners to form sheets parallel to {001}. In addition, 7-and 8-coordinate Ca polyhedra link to the periphery of the sheets yielding thick slabs. Between the slabs are unconnected AsO3(OH) tetrahedra, which link the slabs only via hydrogen bonding. The Raman spectrum shows features consistent with OH and/or H2O in multiple structural environments. The region between the slabs may host excess Al in place of some As. © 2013 Mineralogical Society. Source


Kampf A.R.,Natural History Museum of Los Angeles County | Nash B.P.,University of Utah | Dini M.,Pasaje San Agustin 4045
Mineralogical Magazine | Year: 2013

The new mineral magnesiokoritnigite (IMA 2013-049), ideally Mg(AsO 3OH)H2O, was found at the Torrecillas mine, Salar Grande, Iquique Province, Chile, where it occurs as a secondary alteration phase in association with anhydrite, chudobaite, halite, lavendulan, quartz and scorodite. Crystals of magnesiokoritnigite are colourless to pale-pink, thin to thick laths up to 2 mm long. Laths are elongated on [001], flattened on {010} and exhibit the forms {010}, {110}, {110}, {101}, {031} and {031}. The crystals also occur in dense deep-pink intergrowths. Crystals are transparent with a vitreous lustre. The mineral has a white streak, Mohs hardness of ∼3, brittle tenacity, conchoidal fracture and one perfect cleavage on {101}. The measured and calculated densities are 2.95(3) and 2.935 g cm- 3, respectively. Optically, magnesiokoritnigite is biaxial (+) with α = 1.579(1), β = 1.586(1) and γ = 1.620(1) (measured in white light). The measured 2V is 50(2) and the calculated 2V is 50. Dispersion is r < v, medium. The optical orientation is Y ≈ b; Z ^ c = 36 in obtuse b (note pseudomonoclinic symmetry). The mineral is non-pleochroic. The empirical formula, determined from electron-microprobe analyses, is (Mg 0.94Cu0.03Mn0.02Ca0.01) Σ 1.00As0.96O5H3.19. Magnesiokoritnigite is triclinic, P1, with a = 7.8702(7), b = 15.8081(6), c = 6.6389(14) Å, α = 90.814(6), β = 96.193(6), γ = 90.094(7) , V = 821.06(19) Å3 and Z = 8. The eight strongest X-ray powder diffraction lines are [d obs Å (I)(hkl)]: 7.96(100)(020), 4.80(54)(101), 3.791(85)(210,210,131,131), 3.242(56)(012,221, 012), 3.157(92)(211,230,230), 3.021(61)(141,141,221,221), 2.798(41)(032,032) and 1.908(43)(multiple). The structure, refined to R 1 = 5.74% for 2360 F o > 4σF reflections, shows magnesiokoritnigite to be isostructural with koritnigite and cobaltkoritnigite. © 2013 Mineralogical Society. Source


Kampf A.R.,Natural History Museum of Los Angeles County | Sciberras M.J.,University of Western Sydney | Williams P.A.,University of Western Sydney | Dini M.,Pasaje San Agustin 4045
Mineralogical Magazine | Year: 2013

The new mineral leverettite (IMA 2013-011), ideally Cu3CoCl 2(OH)6, was found at the Torrecillas mine, Salar Grande, Iquique Province, Chile, where it occurs as a supergene alteration phase in association with akaganéite, anhydrite, chalcophanite, goethite, halite, manganite, pyrite, quartz and todorokite. Crystals of leverettite are steep rhombohedra to 1 mm with {101} prominent and modified by {001}, sometimes forming V-shaped twins by reflection on {102̄}. The crystals can also form finger-like, parallel stacked growths along the c axis. The new mineral is medium to deep green in colour and has a light green streak. Crystals are transparent with a vitreous lustre. Mohs hardness is ~3 and the crystals have a brittle tenacity, a perfect cleavage on {101} and a conchoidal fracture. The measured density is 3.64(2) g cm-3 and calculated density based on the empirical formula is 3.709 g cm-3. Optically, leverettite is uniaxial (-) with o and ε > 1.8 and exhibits pleochroism with O (bluish green) > E (slightly yellowish green). The empirical formula, determined from electron-microprobe analyses is Cu3(Co0.43Cu 0.40Mn0.17Ni0.07Mg0.01) Σ1.08Cl1.87O6.13H6. Leverettite is trigonal (hexagonal), space group R3̄m, unit-cell parameters a = 6.8436(6) and c = 14.064(1) Å, V = 570.42(8) Å3, Z = 3. The eight strongest X-ray powder diffraction lines are [dobs Å(I)(hkl)]: 5.469(90)(101), 4.701(18)(003), 2.905(22)(021), 2.766(100)(113), 2.269(66)(024), 1.822(26)(033), 1.711(33)(220), 1.383(23)(128). The structure, refined to R1 = 0.023 for 183 Fo > 4sF reflections, shows leverettite to be isostructural with herbertsmithite and gillardite. © 2013 The Mineralogical Society. Source

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