FE-57-MOSSBAUER INVESTIGATION ON GARNETS FROM THE IVREA-VERBANO ZONE

A Mossbauer investigation has been carried out on garnets from the Ivr ea-Verbano zone and the results are compared with those obtained on th e same samples by X-ray absorption spectroscopy (XAS). The problem add ressed is the precise structural characterisation of the local environ ment of iron in garnets with Fe/Ca ratio variable between similar to 3 .0 and similar to 18.0. Ferric iron is octahedrally coordinated and fe rrous iron is in the dodecahedral site in all the samples. Mossbauer r esults are in agreement with those obtained by XAS and show that, at l east in the compositional range of the garnets examined (0.1-0.5 calci um atoms p.f.u.), the iron environment is not significantly modified b y the larger calcium cations sharing the same dodecahedral site. It is confirmed that the Mossbauer technique is more sensitive than XAS in detecting low percentages of iron, especially when the cation is prese nt in more than one oxidation state and coordination number.