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Mössbauer studies of synthetic and natural micas on the polylithionite-siderophyllite join |
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| Authors: | Christian Levillain Pierre Maurel Francis Menil |
| Institution: | 1. Groupement d'Intérêt Scientifique B.R.G.M.-C.N.R.S., 1A, rue de la Férollerie, F-45045, Orleans Cedex, France 2. Centre de Recherches sur la Synthèse et la Chimie des Minéraux, 1A, rue de la Férollerie, F-45045, Orleans Cedex, France 3. Laboratoire de Chimie du Solide, Université de Bordeaux, 351, cours de la Libération, E-33405, Talence, France |
| Abstract: | Mössbauer studies of micas on the polylithionite-side-rophyllite join show the existence of a relation between the quadrupole splitting (ΔE Q) values of Fe2+ high spin doublets and both cationic and anionic composition of micas. This linear relation is positive as Li2O content increases and negative as F content increases. In the lithium iron micas, the inner ferrous quadrupole doublet is assigned to the cis-site M(2), while the outer doublet is assigned to the trans-site M(1). A random distribution of Fe2+ is observed in fluorine-rich compositions, while slight enrichment of the M(1) site is noticed in hydroxyl compositions, perhaps due to a more sensitive oxidation in situ in M(2) than M(1) sites. The Mössbauer spectrum of siderophyllite K2(Fe 4 2+ Al2)(Si4Al4)O20(OH)4 shows the presence of only one ferrous doublet, which is assigned to M(2) sites. Hence from Mössbauer data we must consider a clintonite (“xanthophyllite”) structure for this mica. The ordered octahedral layer has two distorted ferrous cis-sites and one, more symmetrical, aluminum trans-site. |
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