ABSTRACT LXXIV, SEPTEMBER 2005 n.2:

PIERRE OZER and GABRIELLA LUCCHETTI - Aeolian dust falls in northern Italy in autumn 1996: chemical and mineralogical comparison

Abstract - This paper describes two dust fall events in Genoa and Turin (northern Italy) on 12 November 1996 and 7 December 1996 respectively. Meteorological data suggest that the dust-bearing rain that fell on Genoa originated in north-eastern Morocco, where dust mobilisation was reported two days earlier, and had been carried straight to the north-western Italian coast by very strong winds. But the dust fall observed in Turin was not characterised by any specific synoptic situation inducing dust transport from the southern Mediterranean. The analyses include a quantitative and a qualitative study of two dust samples collected in downtown Genoa and Turin. The total amounts of dust that fell give two very high values of 4.05 g m^-2 for Genoa and 0.54 g m^-2 for Turin. The median sizes of the dust particles were 14.6 µm and 25.8 µm respectively. Most of the dust material collected in Genoa showed a yellowish-brown to red colour due to surface weathering by ferric hydroxides, and was sometimes coated with clayey particles. This attests to the Saharan origin of the particles. On the contrary, only 15% of the material sampled in Turin was coated with red-like clayey material from the desert. A large part of the sample was covered with a carbon-like substance. In addition, the proportion of organic matter (pollen grains and seeds) and anthropogenic fibrous material was much higher. This suggests that the dust fall observed in Turin very likely originated from local pollution mixed with a low proportion of long-distance Saharan dust.

Abstract - This study contributes to the knowledge of the compositional, mineralogical, microstructural and physical characteristics of the Apuan marbles, focusing the attention on the existing relationships among these different parameters. For this purpose samples of marble, primarily white, coming from different zones of the Apuan Metamorphic Complex, were investigated.
The studied samples show homogeneous chemical-mineralogical composition. They are characterised by high CaO content, low SiO₂, Al₂O₃, MgO and Fe₂O₃ amounts. On the other hand, it is clear that the microstructural characteristics vary not only among different basins (e.g., Carrara and Arni basins), but also within a same basin. This is the result of the complex tectono-metamorphic history suffered by the Apuan marble. Samples characterised by grain boundaries from straights to slightly lobates without shape orientation, up to terms characterised by strong orientation and grain boundaries from interlobates to strongly sutured were analysed.
Microstructural parameters were measured through image analysis methods in order to quantify the mean grain size and its distribution and to evaluate the presence of crystals shape orientation and the grain boundaries convolution. The different microstructural characteristics were connected with the main physical characteristics of the stone material: total open porosity, mesoporosity, pore size distribution, imbibition coefficients, saturation indexes, trends of saturation curves obtained from total immersion and capillarity. It’s evident that the microstructural characteristics strongly influence the petrophysical parameters of the examined white marbles.

Abstract - In this study spinel data from literature were treated in order to highlight the influence of Fe³⁺/Fe_tot quantification accuracy on estimate of upper mantle f_O2. Particular regard was given to the importance of using recoil-free fraction f on Fe³⁺/Fe_tot ratios quantification derived from ⁵⁷Fe Mössbauer spectroscopy analysis (MS). For this aim Fe³⁺/Fe_tot ratios obtained by ⁵⁷Fe Mössbauer spectroscopy at 298 K (RT) were corrected with f values calculated by De Grave and Van Alboom (1991). Uncorrected and corrected Fe³⁺/Fe_tot ratios allowed to calculate f_O2 by using oxygen geobarometric method. Oxygen fugacities derived by the uncorrected ratios are revealed systematically higher than those derived by corrected ones, with a difference up to 0.7 log f_O2 units. By using chemical data from two literature works it was highlighted that f_O2 overestimate is not dependent neither on rock chemical composition nor on the equilibrium phases involved in the calculation, but only on the Fe³⁺/Fe_tot ratios quantification accuracy.