Iron distribution in some Italian tuffs

The structural configuration of iron (oxidation state, coordination, distribution) in four representative Italian tuffs (from Campania and Sicily) has been investigated by means of Mössbauer spectroscopy. The octahedrally coordinated high-spin Fe2+ ions in all tuff samples are present in considerably lower amounts than in most other natural alumina silicates and are fewest in Campanian tuffs. In the latter, Fe3+ occupies both tetrahedral and octahedral sites, in Sicilian tuff only tetrahedral positions. The higher Fe3+ contents of Campanian tuffs stand in relation to the greater zeolite content. Ancillary iron oxides are eventually present with particle size below ?200Å.