| 高铁铁橄榄石的新研究——兼论铁橄榄石的氧化作用 |
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| STUDY OF FINE TEXTURES OF FERRIFAYALITE AND DISSCUSION ON OXIDATION OF FAYALITE |
| After ferrifayalite (or laihunite) ,was discovered in one of metamorphic iron ore deposits of north-east China (Ferr. Res. Grpup, 1976; Lai. Res. Group, 1976), a few detailed studies on this mineral have been made by many mineralogists at home and abroad (Shen et al. 1981; Zhang et al. 1981s Martha et al. 1985; Kan et al. 1985). Although there were different points of view, almost all mineralogists identify that ferrifayalite is a new mineral or a distorted olivine type mineral.In this study, many SEM, EPM, TEM, XRD and LARAM work on this mineral have been done. First of all, SEM, EPM was used to check the homogeneity of more than 100 grain ferrifayalites. It is proved that the called ferrifayalite was very heterogeneous from BE, AE, SE and XR images. Two phases can be distinguished at least, in addtion to eulite, magnetite and quartz. One is fayalite. The other is oxidative fayalite. Electron probe microana-lyses of fayalite matrix give a formular Fe1.942+Mg0.05Si1.01O4 without Fe3+ (according to fine structure of Fe L X-ray spectra). But when oxidative fayalite was put under the electron beam, the point, line and area quantitative analysis reaults are significant different one point by one point. Especially the variation in FeO content is from 57.72% to 65.45% without evident concentration in area analysis (46 ×46=2116 points). The EPM total values of a few oxidative fayalites are as low as about 92%, It means all of Fe2+ were oxidized to Fe3+. The lamellaes of glass matter are also discovered in oxidative fayalite by TEM and LARAM. The orientation of lamellaes with respect to the fayalite mainly parallel to (001), but often heterogeneously on small cracks or dislocation.In short, the present SEM, EPM, TEM, XRD and LARAM data give the following new points:1. After forming of fayalite, it was suffered two alterations at least. At first fayalite was altered by oxidation to form intergrowth of eulite, magnetite and quartz. Secondly oxidative fayalite occured as no stoichoimetric alteration product under the high temperature (about .400℃). It is different from oxidation of other olivine (Haggerty et al. 1967; Kohlstedt et al. 1975; Naslund et al. 1983; Putnis, 1979; Wenk et al. 1973).2. Ferrifayalite discovered in China is not a homogeneous phase. Its chemical and physical properties are different even within every individual grain. Originally so called ferrifayalite actually is a mixture of fayalite, oxidative fayalite and a little glass, magnetite, hematite, quartz and so on. The glass matter must be final product of altered fayalite.3. Oxidative fayalite as transitional phase between fayalite and glass even on a micon scale it varies widely in chemical and physical properties with oxidation degree. It seems that a continuous suite between fayalite and glass.4. Lamellaes discovered in so called ferrifayalite in this study is very important.Which one is a new phase? How does the substitution of Fe2+ by Fe3+ dispread in fayalite? It is needed to do more work by TEM and XRD.We wish to express our thanks to Dr. D. Ohnenstetter (CRSCM-CNRS, France), Dr. J. Dubessy (CRGU, France), Dr. H. U. Nissen (ETH Switzerland) Mr. C. Gilles, Mr. J. Breton, Mr. F. Piliard (BRGM, France) for their assistances in doing SEM, EPM, TEM, XRD and LARAM analyses. |
| ZHOU Jian-xiong,Z.Johan.1987.STUDY OF FINE TEXTURES OF FERRIFAYALITE AND DISSCUSION ON OXIDATION OF FAYALITE[J].Acta Geoscientica Sinica,9(3):121-140. |
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