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Aix-en-Provence, France

Grey I.E.,CSIRO | Mumme W.G.,CSIRO | Price J.R.,Australian Synchrotron | Mills S.J.,Khan Research Laboratories | And 2 more authors.
Mineralogical Magazine | Year: 2014

Bariopharmacoalumite-Q2a2b2c, Ba0.5(Cu,ZnO)0.1H0.6[Al4(OH)4(As0.9Al0.1O4)3]·5.5H2O, from the south mine of the old copper mine at Cap Garonne, France, has a 2 × 2 × 2 I-centred tetragonal superstructure of the basic pharmacosiderite-type structure. Cell parameters are a = 15.405(2) Å and c = 15.553(3) Å. The structure was determined and refined in I4¯2m to R 1 = 0.057 for 2697 reflections with I > 2σ(I), using synchrotron X-ray data on a twinned crystal. The origin of the superlattice cell doubling was determined to be due predominantly to the ordering of Ba atoms in half of the [0 0 1] channels, centred at (0, 0, 0) and (1/2,1/2 0). The other channels, centred at (1/2, 0, 0) and (0,1/2, 0), were found to be occupied by corner-connected chains of Cu/Zn-centred square planar units. © 2014 Mineralogical Society.

Meisser N.,University of Lausanne | Brugger J.,University of Adelaide | Brugger J.,South Australian Museum | Krivovichev S.,Saint Petersburg State University | And 2 more authors.
European Journal of Mineralogy | Year: 2012

Maghrebite, MgAl2(AsO4)2(OH) 2·8H2O, is a new mineral occurring at the Aghbar open pit mine, Bou Azzer district, Anti-Atlas, Morocco. Maghrebite is associated with quartz, erythrite, arseniosiderite, wendwilsonite and cabalzarite, and results from the weathering of a Variscan hydrothermal Co-Ni-As-(Cu-U-Mo) vein. Maghrebite forms lozenge-shaped prismatic crystals up to 0.2mm in length. It is colorless, translucent with vitreous luster. Dmeas is 2.60 (1) g/cm3, Dcalc (crystal structure) 2.46 g/cm3. The new mineral is biaxial negative without pleochroism. Measured 2V angle is 87 (3)°; the refractive indices measured at 589 nm are: α = 1.562 (2), β = 1.574 (2), γ = 1.586 (2) with the following orientation α // b; β ∧ c = 28.8° and γ ∧ a = 25.5°. The empirical chemical formula is (Mg0.96Co0.01Ca0.01) ∑=0.98(Al1.94Fe0.06 3+) ∑=2.00(As2.01Si0.01) ∑=2.02H18.0O18.02. Maghrebite is triclinic, P1̄, Z = 1, with a = 5.436 (2)Å, b = 10.500 (3)Å, c=7.075 (2)Å, α =97.701 (7)°, β= 110.295 (5)°, γ= 102.021 (6)° and V= 361.0 (2)Å 3. The six strongest lines in the X-ray powder diffraction pattern are [d in Å (I)(hkl)]: 9.9 (100) (010), 6.4 (90) (001), 4.90 (80) (-101), 3.198 (60) (002), 2.885 (60) (-131) and 2.622 (60) (13-1). The structure was solved by direct methods and refined to R 1=0.045 on the basis of 1064 unique observed reflections. The structure is based upon [Al(AsO4)(OH)(H2O) 3]- layers parallel to (010) and interlinked by [Mg(H 2O)6]+ octahedra. In addition, there is one H2O molecule in the structure that is not bonded to any cation but is held in between the layers by hydrogen bonds only. The topology of the Al arsenate octahedral-tetrahedral layer is that of the laueite type and belongs to the laueite isomer of the laueite-stewartite-pseudolaueite-metavauxite group of structural and geometrical isomers. Maghrebite is an arsenate analogue of gordonite and is the first natural member of the laueite group to contain arsenate as the major anion group. © 2012 E. Schweizerbart'sche Verlagsbuchhandlung, D-70176 Stuttgart.

Mills S.J.,Khan Research Laboratories | Kampf A.R.,Natural History Museum of Los Angeles County | McDonald A.M.,Laurentian University | Favreau G.,421 Avenue Jean Monnet | Chiappero P.-J.,French Natural History Museum
Mineralogical Magazine | Year: 2012

Forêtite, ideally Cu 2Al 2(AsO 4)(OH,O,H 2O) 6, is a new secondary arsenate mineral from the Cap Garonne mine, Var, France (IMA2011-100). It has also been identified at the Salsigne gold mine, Languedoc-Roussillon, France. Although it was identified as a potentially new mineral in 1993, a formal description has only been possible as a result of a new find in a chamber called Annex S located near the entrance of the Cap Garonne mine. Forêtite occurs as pale sky blue to aqua aggregates, up to ∼0.1 mm across, made up of minute plates no more than 20 μm in length. It has a very pale blue streak. Individual crystals have a vitreous lustre and are transparent, whereas clusters appear translucent. The calculated density is 3.286 g cm -3. The crystals are brittle, with an irregular fracture and have a hardness of ∼3-4 on Moh's scale. Forêtite is found in direct association with bariopharmacoalumite, cyanotrichite, parnauite, chalcophyllite and mansfieldite in an Al-rich assemblage which is presumed to have formed under acidic conditions. It is biaxial; the average refractive index measured in white light on aggregates of forêtite crystals is 1.620(5). The empirical formula (based on 10 oxygen atoms per formula unit) is Cu 1.94(Al 1.96Fe 0.04) Σ2.00(As 0.84S 0.09Si 0.04) Σ0.97O 10H 5.19. Raman spectroscopy confirms the presence of OH and H 2O in the structure. Forêtite is triclinic, space group P1, with a = 6.969(9), b = 7.676(9), c = 8.591(11) Å, α = 82.01(9), β = 71.68(8), γ = 102.68(8)°, V = 415(1) Å 3 and Z = 2. The five strongest lines in the X-ray powder diffraction pattern [d in A ̊ , (I), (hkl)] are as follows: 7.307, (100), (010, 01̄0); 3.141, (24), (200, 2̄00); 2.818, (24), (22̄0, 2̄20); 4.519, (23), (111); 2.343, (22), (13̄1). The mineral is named in honour of Dr Jean-Paul Forêt, who co-founded the project that turned the Cap Garonne mine into a protected site and museum. © 2012 Mineralogical Society.

Mills S.J.,Khan Research Laboratories | Christy A.G.,Australian National University | Kampf A.R.,Natural History Museum of Los Angeles County | Housley R.M.,California Institute of Technology | And 3 more authors.
Mineralogical Magazine | Year: 2012

Zincalstibite-9R, a new polytype in the hydrotalcite supergroup is reported from the Monte Avanza mine, Italy. It occurs as pale blue curved disc-like tablets flattened on {001} intergrown to form rosettes typically less than 50 μm in diameter, with cyanophyllite and linarite in cavities in baryte. Zincalstibite-9R is uniaxial (-), with refractive indices ω = 1.647(2) and ε = 1.626(2) measured in white light. The empirical formula (based on 12 OH groups) is (Zn2+ 1.09Cu2+ 0.87Al0.04)Σ2.00Al1.01(Sb 5+ 0.97Si0.02)Σ0.99(OH) 12, and the ideal formula is (Zn,Cu)2Al(OH) 6[Sb(OH)6]. Zincalstibite-9R crystallizes in space group R3, witha = 5.340(2),c = 88.01(2) Å,V = 2173.70(15) Å3 and Z = 9. The crystal structure was refined to R 1 = 0.0931 for 370 unique reflections [F o > 4σ(F)] and R 1 = 0.0944 for all 381 unique reflections. It has the longest periodic layer stacking sequence for a layered double hydroxide compound reported to date. © 2012 Mineralogical Society.

Mills S.J.,University of British Columbia | Mills S.J.,Khan Research Laboratories | Whitfield P.S.,NRC Institute for Chemical Process and Environmental Technology | Kampf A.R.,Natural History Museum of Los Angeles County | And 5 more authors.
Journal of Geosciences (Czech Republic) | Year: 2012

The crystal structures of the 3R polytypes of takovite and woodallite are presented. The structure of takovite was solved on a single crystal from the Agoudal mine, Bou Azzer district, Tazenakht, Morocco to R1 = 1.87% for 94 unique reflections [Fo>4σF] in R3̄m, with unit cell parameters a = 3.0290(2) and c = 22.5995(15) Å. The crystal structure of woodallite [space group R3̄m, with unit cell parameters a = 3.10124(8) and c = 23.6817(16) Å] was refined utilising the Rietveld method on a sample from the MKD5 orebody at the Mount Keith Nickel Mine, Western Australia.

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