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The Structural Formula of Talc from the Trimouns

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The Structural Formula of Talc from the Trimouns 997 TheCanatlian Mineralo gist Vo].37, pp. 997-1006 (1999) THESTRUCTURAL FORMULA OF TALCFROM THE TRIMOUNS DEPOSIT, PYRENEES.FRANCE FRANQOIS MARTIN$ ANDPIERRE MICOUD Inboratoire de Mindralogie,Universitd Paul Sabatier-Toulouse III, UMR 5563du CNRS,39, Alldes Jules Guesde, F-31000 Toulouse. France LUC DELMOTTE, CLAIRE MARICHAL ANDRONAN LE DRED LaboratoireMatdrieux Mindraux, URA 0428, CNRS, Ecole Nationale Supdrieure de Chimiede Mulhouse, j, rueAlfred Werner,F-68093 Mulhouse Ceder, France PHILIPPE DE PARSEVAL Laboratoirede Mindralogie,Universitd Paul Sabatier-Toulouse III, UMR 5563du CNRS,39, All4es Jules Guesde, F-31000 Toulouse. France ALAIN MARI ktboratoire de Chimiede Coordination,CNRS,205 Route de Narbonne,F-31077 Toulouse Cedex, France JEAN-POL FORTUNE, STEFANO SALVI ANDDIDIER B6ZIAT Laboratoirede Mindralogie,Universitd Paul Sabatier ToulouseIII, UMR 5563du CNRS,39, All4es Jules Guesde, F-31000 Toulouse, France OLIVIER GRAUBY Centrede Recherche de la Moddlisationet de la CroissanceCristalline, CNRS, Campus de Luminy,Case 913, F-13288Marseille Cedex 9. France JOCELYNEFERRET Talc de Luzenac 5.A., BP 1162, F-31036 Toulouse Ceder, France Assrnacr A sample of talc (Tl 11) from the Trimouns deposit, in the Pyr6n6es,France, was studied by various spectroscopicmethods (FTIR, NMR, EPR and M<issbauer),as well as HRTEM and X-ray diffraction, in order to investigate the extent of minor substi- tutions in the tetrahedraland octahedral sites. Substitutions causea deficiency in tetrahedralcharge, compensated by an excessin octahedral charge, ensuring an electroneutrality of the structue The charge deficiency on the layer of tetrahedra explains the active interaction between talc (used as filler) and polymer. Keywords: talc, tetrahedral site, octahedral site, substitutions, spectroscopy,charge deficiency, polymer, Trimouns, Pyr6n6es SovuaInB Un 6chantillon de talc (T111) provenant du gisement de Trimouns (Pyr6n6es,France) a 6t6 6tudi6 en d6tail d l'aide des spectroscopiesFTIR, NMR, EPR et Mijssbauer, du microscope 6lectronique d transmissionet de la diffraction des rayons X afin de quantifier les faibles taux de substitution dans les sites tdtraddriqueset octa6ddques.Les r6sultats monffent que le feuillet du talc Tl 1I est 6lectriquement neutre, avec un d6ficit de charge t6traddrique compens6par un excds de charge octa6drique, ceci 6tant d0 aux nombreusessubstitutions. Le d6ficit local de surface de la couche t6tra6driquepeut expliquer les interactions actives entre le talc, utilis6 comme charge min6ra1e,et les polymdres. Mots-clis: talc, site tefa6drique, site octa6drique,substitutions, spectroscopies, d6ficit de charge,polymdres, Trimouns, Pyr6n6es. s E-mail address: [email protected] 998 THE CANADIAN MINERALOGIST INrnooucrroN due to inclusions of graphite. The total iron content of the talc ore is about 0.6 ! O.2VoFe2O3, but no separate Talc ore is used in paper coating, and its properties iron-bearing phase has been detected. make it useful in the paint, ceramics, and polymer industries. In the automotive industry, talc is added to ANarvrrcer MBrnoos polymers to stabilize and harden parts of automobiles like fenders, dashboard,and steering wheel. However, Chemical analyses various problems appear with these materials, notably an undesirable coloring in ceramics and polymers Whole-rock analysis were performed by Inductively (blush), and variable behavior in polymer applications. Coupled Plasma (ICP) at the CRPG in Nancy. The To improve the use of various types of talc in specific chemical composition of the talc was determined using industrial applications, it is necessary to take into a CamecaSX-50 electron microprobe at the Universitd account the physical and chemical propertiesofthe talc. Paul Sabatier in Toulouse. Operating conditions were In this paper, we characterizethe chemical composition 15 kV and 10 nA, and natural and synthetic standards of a sample of pure talc (T111) from the Trimouns were used. deposit,the largestofthe world. The resultsofthis study X-ray dffiaction (XRD) improve our knowledge of the extent of substitutionsin talc from this deposit by detailed characterization of The talc from the Trimouns deposit was analyzedby element distributions (Fe2+,Fe3+, Al, Mn2+, F), using X-ray diffraction (XRD). The spectrawere collected in variousspectroscopic techniques. reflection mode using a Philips PWl130 diffractometer with Ni-filtered CuKct radiation (30 kV, 30 mA). The BecrcnouNo lNpouaarron spectrawere recorded for 3.5 s per step of 0.0005" from 2' to 80' (e). With this approach,the limit of detection Most samples of talc (2:7 layer silicate) typically of a phasewas establishedat0.5Vo. have a near-end-member composition [Mg3Si4O1e (OH)zl, and in many casesno interlayer exists because Fourier transform infrared spectroscopy( FTIR) the 2:7 layer is electrostatically neutral. However, ma- j or amounts of Fe, minor amounts of Al and F, and faces Fourier transform infrared (FTIR) spectra were of Mn, Ti, Cr, Ni, Na and K have been reported in talc recorded in transmission mode in the 4000-400 cm 1 (Heller-Kallai & Rozenson 1981, Noack et al. 1986, range on a Nicolet 510 FTIR spectrometer.The pellets Abercrombie et al. 198'7, Aramt et al. 1989, Coey et al. were prepared by mixing 4 mg sample with 300 mg L997, de Parsevalet al. 1991,1993). These authors KBr. documented the various potential substitutions in the tetrahedral(Si replacedby Fe3+,Al) and octahedralsites s7Fe Mdssbauer spectroscopy (Mg replaced by Fe2*, Fe3*, A1), but did not establish charge balance of these natural samplesof talc. A 57FeMossbauer absorption spectnrm was recorded over the range!4 mm/s with 512 channelsin the Labo- GBorocrcer- Coxrsxr ratoire de Chimie de Coordination in Toulouse. The Mrissbauer spectrometeris composed of a compact de- The Trimouns talc and chlorite deposit is located rn tector "y-systemfor high count-ratesand a conventional the French Pyr6n6es, 100 km south of Toulouse, at an constant-accelerationMtissbauer device (WISSEL). A 57Co altitude of 1,700 m. It occurs along the eastem side of 1in Rh) source with nominal activity of 50 mCi the Hercynian Saint Barth6l6my Massif of gneissic was used. Powders were finely ground under acetone rocks. The mode of formation of the talc and chlorite rn (to minimize possible oxidation of Fe) and placed in a the deposit is now well established(Fortun6 et a|.7980, plexiglass sample holder. The spectrawere obtained at Moine et al. 1982, 1989, de Parsevalet al. 1993). These room temperature, 80 K and 4 K, and, were recorded minerals originated by hydrothermal alteration of with a Canberra multichannel analyzer, coupled to a wallrock in a zone of intenseshearing between the Saint computer. The isomer shift was recorded with respect Barth6l6my dome and the low-grade Paleozoic meta- to cr-Fe metal. As advocatedby Rancourt et al. (1993), morphic cover. Dolostones of the Paleozoic cover were the absorber thickness ofthe talc sample was approxi- transformed to talc, whereas siliceous and aluminous mated to that of micas in the phlogopite-annite series; rocks (mica-bearing schists and granitic pegmatites) in particular, phlogopite has a Fe content similar to that were completely transformed to chlorite-dominant ore of talc T1 I l. This was done to minimize the width of characterizedby well-defined metasomatic zones. The the absorptionlines in the^spectra.The values are around transformation of dolostone to talc involved addition of 200 mg of mineral per cm'. Lorentzian line-shapeswere Si, leaching of Ca, and loss of CO2during the alteration. assumedfor deconvolutions.based on least-squares The talc ore exhibits facies that vary in color from pure fitting procedures.The r!2 and misfrt values were used white to grey and to black, the latter being principally to measurethe goodnessof the computer fit. THE STRUCTURAL FORMULA OF TALC FROM TRIMOUNS, FRANCE 999 Electron paramagnetic resonance( EPR) spectroscopy TABLE 2 CHEMICAT COMPOSITIONO}- TALC TI I ] All EPR spectrawere recorded at room temperature with a Bruker ESP-300e spectrometeroperating at AlrO: 009 019 X-band frequency (9 GHz). A mercury lamp was used Fe2OrG) 059 068 as UV radiation source (200 W), iradiating the ESR MnO o02 fr 023 Mco 3t 1l 3152 TI cavity through the medium of a quaftz optical fiber. This CaO 002 002 4 60 4.84 procedureallowed us to follow the evolution ofthe ESR Na2O 001 Tr 9961 99 03 on l0 points spectrum of the sample during the UV irradiation. ICP : lnductively Coupled Plasma Nuclear magnetic resonance( NM R) spectroscopy Rssur-rs The solid-state nuclear magnetic resonanceexperr- ments were performed as follows: 29SiNMR measure- Chemicnlcomposition ments were carried out on a Bruker MSL-30 '7.1 spectrometeroperated atBo - T (u6= 59.63 MHz) The talc sample was selected from a vein of pure with B0 the magnetic field. The NMR spectra of 27Al talc; it is representativeof ore in the Trimouns deposit, and leF were recorded on a Bruker DSX-400 spectrom- and was carefully hand-picked. Its chemical composr- eter operating at B0 = 9.4 T (vo= 104.263 and 376.49 tion (Table 2) indicates a virtually monominerallc MHz, respectively).Single-pulse magic-angle spinning sample, with no accessoryminerals and no Fe-bearins (MAS) spectra were obtained using a Bruker MAS minerals, such as sulfides. probe with a 7 mm Zro2rotor for the 2eSiexperiment and a 4 mm rotor for the 27Al and l9F experiments. XRD Acquisitions parameters are summarized in Table 1. Chemical shifts of ze5i, zr41 and 1eFwere externally The powder-diffraction pattern is characteristic
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