Aix-en-Provence, France
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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.,University of British Columbia | Rumsey M.S.,Natural History Museum in London | Favreau G.,421 Avenue Jean Monnet | Spratt J.,Natural History Museum in London | And 2 more authors.
Mineralogical Magazine | Year: 2011

Bariopharmacoalumite, ideally Ba 0.5Al 4(AsO 4) 3(OH) 4•4H 2O, is a new mineral from Cap Garonne, France. It occurs in several places within the mine as colourless to pale yellow interpenetrating cubes up to 0.5 mm across. Bariopharmacoalumite is transparent to translucent, with a white streak, has an adamantine lustre and imperfect cleavage on {001}. The Vickers hardness is 234.35 and the Mohs harness is 3.5. Bariopharmacoalumite is isotropic, with n = 1.573 (upper estimate) [calculated from reflectance values at 589 nm using Fresnel Equations]. The empirical formula, based on 20 oxygen atoms, is: (Ba 0.54Cu 0.03K 0.01) Σ0.58(Al 3.99Fe 0.02) Σ4.01(AsO 4) 3.00(OH) 3.85O 0.15•4H 2O and the calculated density (on the basis of the empirical formula and single-crystal unit cell) is 2.580 g/cm 3. The four strongest lines in the X-ray powder diffraction pattern are [d obs(Å), I obs,(hkl)]: 7.759, 100, (001); 5.485, 27, (011); 3.878, 27, (002); 4.454, 18, (011). Bariopharmacoalumite from Cap Garonne is cubic, space group P43m with a = 7.742(4) Å, V = 464.2(4) Å 3 and Z = 1. The crystal structure was solved by direct methods and refined to R 1 = 0.0705 for 215 reflections with I > 4σ(I) and is consistent with members of the pharmacosiderite supergroup. Data are also presented from zoned bariopharmacoalumite-bariopharmacosiderite crystals found at the Mina Grande mine, Chile. © 2011 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.


Biagioni C.,University of Pisa | Moelo Y.,University of Nantes | Favreau G.,421 avenue Jean Monnet | Bourgoin V.,24 rue Mozart | Boulliard J.-C.,University of Paris Descartes
Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials | Year: 2015

The crystal structure of a specimen of 'Pb-rich' chabournéite from Jas Roux, Hautes-Alpes, France, with the chemical formula obtained by electron microprobe analysis of Ag0.04 (1)Tl2.15 (2)Pb0.64 (1)Sb5.12 (1)As5.05 (1)S17.32 (5), has been solved by X-ray single-crystal diffraction on the basis of 36 550 observed reflections (with F o > 4σF o) with a final R 1 = 0.074. Pb-rich chabournéite is triclinic P1, with unit-cell parameters a = 8.5197 (4), b = 42.461 (2), c = 16.293 (8) Å, α = 83.351 (2), β = 90.958 (2), γ = 84.275 (2)°, V = 5823 (3) Å3. Its structural formula is close to [Tl2(Pb0.8Tl0.1Sb1.1)](Sb4.1As4.9)S17, with Z = 8. Its crystal structure is formed by the alternation of two pairs of slabs along the b axis, deriving from the SnS and PbS archetypes, respectively. 104 independent cation sites and 136 S sites occur in the unit cell. Slab interfaces show the alternation, along c, of Tl sites, ninefold coordinated, with Pb, Sb or mixed/split (Pb,Sb) and (Pb,Tl) sites. Within the slabs, 72 independent M 3+ sites (M 3+ = As, Sb) occur. Considering M 3+ - S bond distances shorter than 2.70 Å, MS3 triangular pyramidal groups are condensed according to various Mm S n chain fragments ('polymers'). The solution of the crystal structure of chabournéite allows its comparison with the closely related homeotypes protochabournéite and dalnegroite. © 2015 International Union of Crystallography.


Mills S.J.,Khan Research Laboratories | Kampf A.R.,Natural History Museum of Los Angeles County | Housley R.M.,California Institute of Technology | Favreau G.,421 Avenue Jean Monnet | And 5 more authors.
Mineralogical Magazine | Year: 2012

Omsite (IMA 2012-025) is a new mineral from the Correc d'en Llinassos, Oms, Pyrénées-Orientales Department, France. It occurs as bright yellow to amber yellow discoidal tablets, flattened on {001}, which form rosettes typically 50-100 μm in diameter. Omsite generally crystallizes on siderite without associated supergene minerals; it occurs less commonly with glaukosphaerite. Crystals have a vitreous to resinous lustre, and are transparent to translucent. Omsite is not fluorescent in either short-wave or long-wave ultraviolet light. It has an estimated hardness of 3 on the Mohs' scale, is brittle with an irregular fracture, and has one poor cleavage on {001}. The calculated density is 3.378 g cm-3. Crystals are uniaxial (-), with indices of refraction of ω = 1.728(3) and ε = 1.66(1), measured in white light. Pleochroism is ω = orange-yellow, ε = pale orange-yellow; ω > ε. The empirical formula [based on 12 (OH + Cl) p.f.u.] is (Ni2+ 1.099Cu2+ 0.665Mg0.107Fe3+ 0.045) Σ 1.916Fe3+ 1.000(Sb5+ 0.947As0.072Na0.029) Σ1.048OH11.967Cl0.033. Omsite crystallizes in space group P3, with unit-cell parameters a = 5.3506(8), c = 19.5802(15) Å, V = 485.46(10) Å3 and Z = 2 determined by single crystal X-ray diffraction. The five strongest lines in the X-ray powder diffraction pattern [d in Å, (I rel), (hkl)] are as follows: 4.901, (100), (004); 4.575, (83), (011); 2.3539, (81), (114); 1.8079, (48), (118̄); 3.781, (34), (103). The crystal structure was solved to R 1 = 0.0896 for 356 observed reflections [F o>4σF o] and 0.1018 for all the 469 unique reflections. Omsite is a layered double hydroxide (LDH) mineral, with a topology consistent with members of the hydrotalcite supergroup and cualstibite group. © 2012 Mineralogical Society.


Kampf A.R.,Natural History Museum of Los Angeles County | Mills S.J.,University of British Columbia | Rossman G.R.,California Institute of Technology | Steele I.M.,University of Chicago | And 2 more authors.
European Journal of Mineralogy | Year: 2011

The new mineral afmite, Al 3(OH) 4(H 2O) 3(PO 4)(PO 3OH)-H 2O, is triclinic with space group P1l and cell parameters a = 7.386(3), b = 7.716(3), c=11.345(4) Å, α = 99.773(5), β = 91.141(6), γ = 115.58(5)°, V= 571.6(3)Å 3and Z = 2. It occurs, sometimes in association with matulaite and variscite, in fractures and solution cavities in shale/siltstone at Fumade, Tarn, France. The formation is probably largely the result of remobilisation and crystallisation during low-temperature hydrothermal activity and/or weathering and ground water activity. Afmite forms in cockscomb aggregates of diamond-shaped tablets on {001}, ubiquitously contact-twinned on {001} and also commonly twinned by rotation on [010] with {010} and {11̄0} composition planes, forming star-like sixlings. The streak of the mineral is white, the luster is pearly, and the Mohs hardness is about 11/2 The mineral is flexible, but not elastic, has an irregular fracture and three cleavage directions: {001} perfect, {010} and {110} good. The measured density is 2.39(3) g/cm 3 and the calculated density is 2.391 g/cm 3 based upon the empirical formula. Optical properties (white light): biaxial (+), α = 1.554(1), β = 1.558(1), γ = 1.566(1), 2V meas. = 70(5)° and 2V calc = 71°. Electron microprobe analyses provided Al 2O 3 40.20 and P 2O 5 38.84 wt% and CHN analyses provided H 2O 25.64 wt%, total 103.68 wt%. Normalized EMP analyses and water based on the structure yield Al 2O 3 36.41, P 2O 5 35.17 and H 2O 28.42, total 100.00 wt%. Infrared and Raman spectra were consistent with the PO 3OH, OH and H 2O as indicated by the crystalstructure determination. The strongest powder X-ray diffraction lines are [d obs.(Å),I obs,(hkl)]: 11.089, 100,(001), 3.540,81,(0Ī3,1̄1̄2), 5.484,79,(002,101), 2.918,60(1̄22), 3.089,33(1̄13,201), 4.022,30,(102,1̄12), 6.826,23,(010). The crystal structure, solved from twinned data, (R 1 = 10.4% for 1262 F 0 > 4σF reflections) consists of chains of AlO 6 octahedra parallel to [110] in which edge-sharing octahedral dimers share corners with individual octahedra. Both PO 4 and PO 3OH tetrahedra link the chains into sheets parallel to {001} and the PO 4tetrahedra further serve to link two sheets together into a thick slab in which tetrahedral (T) and octahedral (O) layers alternate, forming a T-O-T-O-T sandwich. The linkage between these sandwiches in the c direction is via hydrogen bonding with isolated H 2O groups in the interlayer region. Afmite is closely related structurally to the turquoise-group minerals and specifically to planerite. The recently described mineral kobokoboite probably has a closely related sheet structure. © 2011 E. Schweizerbart'sche Verlagsbuchhandlung, D-70176 Stuttgart.


PubMed | University of Nantes, University of Pisa, 421 avenue Jean Monnet, University of Paris Descartes and 24 rue Mozart
Type: Journal Article | Journal: Acta crystallographica Section B, Structural science, crystal engineering and materials | Year: 2015

The crystal structure of a specimen of `Pb-rich chabournite from Jas Roux, Hautes-Alpes, France, with the chemical formula obtained by electron microprobe analysis of Ag(0.04(1))Tl(2.15(2))Pb(0.64(1))Sb(5.12(1))As(5.05(1))S(17.32(5)), has been solved by X-ray single-crystal diffraction on the basis of 36,550 observed reflections (with F(o) > 4F(o)) with a final R1 = 0.074. Pb-rich chabournite is triclinic P1, with unit-cell parameters a = 8.5197(4), b = 42.461(2), c = 16.293(8), = 83.351(2), = 90.958(2), = 84.275(2), V = 5823(3)(3). Its structural formula is close to [Tl2(Pb(0.8)Tl(0.1)Sb(1.1))](Sb(4.1)As(4.9))S17, with Z = 8. Its crystal structure is formed by the alternation of two pairs of slabs along the b axis, deriving from the SnS and PbS archetypes, respectively. 104 independent cation sites and 136 S sites occur in the unit cell. Slab interfaces show the alternation, along c, of Tl sites, ninefold coordinated, with Pb, Sb or mixed/split (Pb,Sb) and (Pb,Tl) sites. Within the slabs, 72 independent M(3+) sites (M(3+) = As, Sb) occur. Considering M(3+)-S bond distances shorter than 2.70, MS3 triangular pyramidal groups are condensed according to various M(m)S(n) chain fragments (`polymers). The solution of the crystal structure of chabournite allows its comparison with the closely related homeotypes protochabournite and dalnegroite.


Mills S.J.,Khan Research Laboratories | Christy A.G.,Australian National University | Schnyder C.,Museum dHistoire Naturelle | Favreau G.,421 Avenue Jean Monnet | Price J.R.,Australian Synchrotron
Mineralogical Magazine | Year: 2014

We present Raman data for camerolaite, cyanotrichite and carbonatecyanotrichite, and using synchrotron single-crystal X-ray diffraction have solved the structure of camerolaite from the Tistoulet Mine, Padern, Aude Department, France. Camerolaite crystallizes in space group P1 with the unit-cell parameters: a = 6.3310(13) Å, b = 2.9130(6) Å, c = 10.727(2) Å, α = 93.77(3)°, β = 96.34(3)°, γ =79.03(3)°, V = 192.82(7) Å3 and Z = 1/3, with respect to the ideal formula from the refinement, Cu6Al3(OH)18(H2O)2[Sb(OH)6](SO4). The crystal structure was solved to R1 = 0.0890 for all 1875 observed reflections [Fo > 4σF o] and 0.0946 for all 2019 unique reflections. The P cell has been transformed into a C-centred cell that aids comparison with that of the structurally related khaidarkanite by a C = 2a P-b P , giving parameters a = 12.441(3), b = 2.9130(6), c = 10.727(2) Å, α = 93.77(3), β = 95.57(3), γ = 92.32(3)° and Z = 2/3 in C1. Edge-sharing octahedral ribbons Cu2Al(O,OH,H2O)8 form hydrogen-bonded layers || (001), as in khaidarkanite. The partially occupied interlayer Sb and S sites of the average structure are in octahedral and tetrahedral coordination by oxygen, respectively. They cannot be occupied simultaneously, which leads to regular alternation of [Sb(OH)6]- and SO4 2- groups in rods || y, resulting in local tripling of the periodicity along y for the Sb(OH)6-SO4 rods. Thus, camerolaite has a 'host-guest' structure in which an invariant host module (layers of Cu-Al ribbons) has embedded rod-like guest modules with a longer periodicity. Coupling between the phases of these rods is only short-range, resulting in diffuse X-ray scattering rather than sharp superstructure reflections. Similar disorder is known for parnauite, and is deduced for other members of the cyanotrichite group (cyanotrichite, carbonatecyanotrichite and khaidarkanite). Group members all share the Cu-Al ribbon module but have interlayer rods of different compositions and topologies; thus, they form a merotypic family. The low symmetry of the camerolaite average structure suggests other possibilities for structure variation in the group, which are discussed. © 2014 Mineralogical Society.


Kampf A.R.,Natural History Museum of Los Angeles County | Mills S.J.,Khan Research Laboratories | Nash B.P.,University of Utah | Thorne B.,3898 S Newport Circle | Favreau G.,421 Avenue Jean Monnet
European Journal of Mineralogy | Year: 2016

Alfredopetrovite, Al2(Se4+O3)3·6H2O, is a new secondary selenite mineral from the El Dragón mine, Antonio Quijarro Province, Potosí Department, Bolivia. The mineral occurs in vugs in a matrix of Co-rich krut'aite-penroseite, dolomite and goethite. Associated minerals are: ahlfeldite, allophane, calcite, chalcomenite, favreauite, felso{combining double acute accent}bányaite, malachite and molybdomenite. Crystals occur in drusy/scaly coatings and compact balls, the latter to 0.5 mm in diameter. Individual crystals are up to about 0.1 mm across. The Mohs hardness of alfredopetrovite is 2 1/2; it has no cleavage, curved fracture and a vitreous lustre. The calculated density based on the empirical formula is 2.504 g cm-3. Alfredopetrovite is uniaxial (+), with ω = 1.554(2) and ε = 1.566(2) (white light), and exhibits no pleochroism. Electron microprobe analyses gave the empirical formula Al1.94Cu0.07Ni0.03Co0.01Se2.95O15H12.16, based on 15 O apfu. Alfredopetrovite is hexagonal, space group P62c, with the unit-cell parameters: a = 8.818(3) Å, c = 10.721(2) Å, V = 722.0(5) Å3 and Z = 2. The eight strongest lines in the X-ray powder diffraction pattern are [dobs/Å (I) (hkl)]: 7.63(55)(100), 6.22(55)(101), 5.37(26)(002), 4.398(40)(110,102), 3.404(100)(112), 2.783(50)(211), 2.606(22)(203), and 1.6609(26)(410,322,314,116). The crystal structure was refined to R1 = 0.0268 for 240 observed reflections [Fo > 4σF]. The structure is comprised of fairly regular AlO6 octahedra and Se4+O3 triangular pyramids. Three Se4+O3 pyramids link two adjacent AlO6 octahedra forming a [Al(H2O)3]2(Se4+O3)3 cluster structural unit. These structural units are bonded to one another only via hydrogen bonds yielding a structure with relatively large channels along [001]. The configuration of the cluster is similar to that of the distinctive unit in the NASICON structure, commonly referred to as a lantern unit. © 2015 E. Schweizerbart'sche Verlagsbuchhandlung.


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.

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