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Identification by RAMAN Microscopy of magnesian vivianite formed from Fe2+, Mg, Mn2+ and PO4 3- in a Roman camp near fort Vechten, Utrecht, The Netherlands

By J.T. Kloprogge, D. Visser, W.N. Martens, Loc V. Duong and R.L. Frost

Abstract

The presence of a magnesian vivianite (Fe2+)2.5(Mg, Mn, Ca)0.5(PO4)2. 8H2O, has been identified in a soil sample form a Roman camp near Fort Vechten, The Netherlands, using a combination of Raman microscopy and scanning electron microscopy. An unsubstituted vivianite and baricite were characterized for comparative reasons. The split phosphate-stretching mode is recognized around 1115, 1062 and 1015 cm-1, while the corresponding bending modes are found around 591, 519, 471 and 422 cm-1. The substitution of Mg and Mn for Fe2+ in the crystal structure causes a shift towards higher wavenumbers compared to pure vivianite. As shown by the baričite sample substitution causes a broadening of the bands. The observed broadening however is larger than can be explained by substitution alone. The low intensity of the water bands, especially in the OH-stretching region between 2700 and 3700 cm-1 indicates that the magnesian vivianite is partially dehydrated, which explains the much larger broadening than the observed broadening caused by substitution of Mg and Mn in vivianite and baričite

Topics: Earth Sciences, baričite, iron phosphate, Raman microscopy, vivianite
Year: 2003
OAI identifier: oai:dspace.library.uu.nl:1874/28653
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