Interpretation of the optical absorption spectrum of
Ni-substituted lizardites

Julg, André; Julg, Odette

doi:10.1180/claymin.1984.019.1.12

Cited by 1 publication

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“…Initial studies of the optical absorption spectra of Ni containing phyllosilicates established the presence of divalent 6-fold coordinated Ni in serpentine and talc (Nussik, 1969), chrysotile (Faye, 1974) and the kerolite-pimelite series (Brindley et al, 1979). The optical spectra have recently been revised on a quantitative basis, which has led to a certain amount of controversy: some investigators have stated that Ni occurs in distorted octahedral sites (Cervelle & Maquet, 1982;Julg & Julg, 1984) whereas others consider that some of the Ni atoms are in 4-fold coordination (Tejedor et al, 1983).…”

Section: Optical Absorption Spectroscopymentioning

confidence: 99%

Nickel-bearing clay minerals: I. Optical spectroscopic study of nickel crystal chemistry

1985

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A B S T R A C T:Nickel crystal chemistry was systematically studied in various phyllosilicates, mainly the natural phases selected from the 'garnierites' of the supergene ore deposits of New Caledonia. Minerals which do not usually occur in New Caledonian parageneses were synthe sised, as they could represent intermediate phases of genetic importance. In the kerolitepimelite series, a linear relationship occurred between the ratio I (13,20~/I(02,11 ) of the hk bands and Ni-content. Diffuse reflectance spectra were used to derive the crystal chemical parameters of Ni. These confirmed its divalent character and its occupation of octahedral sites; the resulting structural distortion was slight and could not be detected in some minerals. There was no optical evidence for Ni atoms in 4-fold coordination. The two main parameters which showed significant variations among the studied phases were site distortion and crystal field stabilization energy (CFSE). Site distortion was at a maximum in trioctahedral smectites and sepiolite. CFSE depended on the mineralogy, crystallinity and chemical composition (Al-content) of the phase. Finally, clay minerals are classified according to the increasing stability of Ni in the octahedral sheet, which has been tentatively related to the geochemical distribution of this element. Secondary minerals are usually enriched vs. primary ones and among them are nepouite and kerolite which exhibit a high CFSE in contrast to sepiolite.Although the green-coloured 'garnierites' have been studied for many years (Faust, 1966), their chemical and structural characteristics are not entirely clear. An accurate study of these hydrous Ni-Mg silicates requires investigations at various microscopic scales, from the study of the relations between the various layers to the determination of the precise nature of the sites occupied by Ni atoms.In this paper we present some results quantifying Ni crystal chemistry, which have been derived from the study of diffuse reflectance spectra of various phyllosilicates. Special emphasis is laid on parameters such as coordination number, site distortion, nickel-oxygen bond covalency and crystal field stabilization energy (CFSE). These results should promote a better understanding of Ni geochemistry during the formation of supergene ore deposits. A subsequent paper will be devoted to the intracrystalline distribution of Ni studied by X-ray absorption spectroscopy in the same phases. EXPERIMENTALPure phases were selected on the basis of X-ray diffraction (XRD) and wet chemical analyses. The ignition losses of minerals previously heated at 110~ (H20 +) were 9 1985 The Mineralogical Society

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Section: Optical Absorption Spectroscopymentioning

confidence: 99%