Raman spectra of Ni–Mg kerolite: effect of Ni–Mg substitution on O–H stretching vibrations

Abstract : The Ni-richmineral phases constituting the Ni-ores in New Caledonia are dominated inmost cases by kerolite–pimelite series, also called talc-like minerals. Despite their economic and geologic interests, the crystallographic structures of these minerals are not fully understood. In order to improve the knowledge of their crystallographic structure, a set of natural talc-like minerals of varying Ni/Mg ratio was selected. A combination of SEM, EMPA, TEM, and Raman analysis shows that the studiedmineral contains only one mineral phase identified as the kerolite–pimelite series. Although kerolite and pimelite are not currently recognized as distinct minerals by the IMA, this study shows that these minerals exist as distinct minerals without any mixed layering with other mineral phases such as serpentine or other sheet silicates. The solid solution between the Ni and Mg endmembers was complete without any gap, corresponding to a Ni–Mgsubstitution in the octahedral sheet. The Raman spectra in the OH stretching vibration region of representative samples covering the whole range of Ni–Mg substitution show a continuous and significant evolution from the Mg to the Ni endmember. The signal was decomposed into nine Gaussian–Lorentzian functions, but the large overlapping of the peaks and the complexity of the band structure prevent any interpretation of the spectra from a structural point of view. Finally, the problemis formalized as amultivariate curve resolution (MCR)which is solved using the Bayesian Positive Source Separation (BPSS) algorithm. This reveals that four possible arrangements of Ni and Mg in the octahedral sheet are encountered, and these arrangements are dependent on the Ni–Mg substitution rate. It also confirms that Raman microspectroscopy can be very efficient in quick evaluation of the Ni content of the mineral.
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Submitted on : Friday, June 19, 2015 - 6:35:56 PM
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Michel Cathelineau, Marie-Camille Caumon, Massei Frédéric, David Brie, Harlaux Matthieu. Raman spectra of Ni–Mg kerolite: effect of Ni–Mg substitution on O–H stretching vibrations. Journal of Raman Spectroscopy, Wiley, 2015, 46 (10), pp.933-940. ⟨10.1002/jrs.4746⟩. ⟨hal-01165711⟩

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