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The occurrence of phlogopite and amphibole in mantle ultramafic rocks is widely accepted as the modal effect of metasomatism in the upper mantle. However, their simultaneous formation during metasomatic events and the related sub-solidus equilibrium with the peridotite has not been extensively studied. In this work, we discuss the geochemical conditions at which the pargasite-phlogopite assemblage becomes stable, through the investigation of two mantle xenoliths from Mount Leura (Victoria State, Australia) that bear phlogopite and the phlogopite + amphibole (pargasite) pair disseminated in a harzburgite matrix. Combining a mineralogical study and thermodynamic modelling, we predict that the P–T locus of the equilibrium reaction pargasite + forsterite = Na-phlogopite + 2 diopside + spinel, over the range 1.3–3.0 GPa/540–1500 K, yields a negative Clapeyron slope of -0.003 GPa K–1 (on average). The intersection of the P–T locus of supposed equilibrium with the new mantle geotherm calculated in this work allowed us to state that the Mount Leura xenoliths achieved equilibrium at 2.3 GPa /1190 K, that represents a plausible depth of ~ 70 km. Metasomatic K-Na-OH rich fluids stabilize hydrous phases. This has been modelled by the following equilibrium equation: 2 (K,Na)-phlogopite + forsterite = 7/2 enstatite + spinel + fluid (components: Na2O,K2O,H2O). Using quantum-mechanics, semi-empirical potentials, lattice dynamics and observed thermo-elastic data, we concluded that K-Na-OH rich fluids are not effective metasomatic agents to convey alkali species across the upper mantle, as the fluids are highly reactive with the ultramafic system and favour the rapid formation of phlogopite and amphibole. In addition, oxygen fugacity estimates of the Mount Leura mantle xenoliths [Δ(FMQ) = –1.97 ± 0.35; –1.83 ± 0.36] indicate a more reducing mantle environment than what is expected from the occurrence of phlogopite and amphibole in spinel-bearing peridotites. This is accounted for by our model of full molecular dissociation of the fluid and incorporation of the O-H-K-Na species into (OH)-K-Na-bearing mineral phases (phlogopite and amphibole), that leads to a peridotite metasomatized ambient characterized by reduced oxygen fugacity.

Among asbestos minerals, fibrous riebeckite (crocidolite) and tremolite share the amphibole structure but largely differ in terms of their iron content and oxidation state. In asbestos toxicology, iron-generated free radicals are largely held as one of the causes of asbestos malignant effect. With the aim of clarifying i) the relationship between Fe occurrence and asbestos surface reactivity, and ii) how free-radical generation is modulated by surface modifications of the minerals, UICC crocidolite and fibrous tremolite from Maryland were leached from 1 day to 1 month in an oxidative medium buffered at pH 7.4 to induce redox alterations and surface rearrangements that may occur in body fluids. Structural and chemical modifications and free radical generation were monitored by HR-TEM/EDS and spin trapping/EPR spectroscopy, respectively. Free radical yield resulted to be dependent on few specific Fe2+ and Fe3+ surface sites rather than total Fe content. The evolution of reactivity with time highlighted that low-coordinated Fe ions primarily contribute to the overall reactivity of the fibre. Current findings contribute to explain the causes of the severe asbestos-induced oxidative stress at molecular level also for iron-poor amphiboles, and demonstrate that asbestos have a sustained surface radical activity even when highly altered by oxidative leaching.

A reappraisal of crystal structure, optical properties and technological behaviour of black spinels in the Co--Cr--Fe--Mn system was carried out to define the best compositions and disclose the role of crystal chemistry in colouring performance and pigment-glaze interactions. Twenty ternary and quaternary spinel formulations were designed using crystallochemical criteria and prepared by simulating the industrial synthesis. Powder samples were characterized through X-ray diffraction (Rietveld), optical, Raman and Mössbauer spectroscopies, and technological testing in several glazes and glassy coatings. Black spinels fall in a relatively narrow field of unit cell and inversion parameters in between "chromites" and "magnetites". Their cation distribution is governed by Co2+ occupancy of tetrahedrally-coordinated site T and Cr3+ occupancy of octahedrally-coordinated site M, with Mn3+ hosted at M, while Mn2+ and Fe3+ are distributed over both sites. Nevertheless, Raman and Mössbauer spectra indicate a growing disorder in cation partitioning going towards the iron-rich terms. The pigment technological behaviour depends to a large extent on crystal chemistry of spinels, with no effect by grain or crystallite size. The best colouring performance corresponds to recommended compositions able to withstand corrosion and change in crystal chemistry in contact with melted glaze. Three different pathways can give rise to excellent black pigments: (a) strongly disordered spinels having an inversion parameter i~0.2; (b) moderately disordered spinels, free of Mn3+, with i

Fe-ZSM-5 and Fe-S-1 catalysts are active for some reactions of great concern as the one-step selective oxidation of benzene to phenol by N2O [1], the selective catalytic reduction (SCR) of NO and N2O by hydrocarbons,and the catalytic N2O decomposition [2-4]. The catalytic activity has been found to depend on the nature of the iron species formed upon calcination in air at high temperature. ln order to clarify the formation process and the nature of the FexOy-like species, we prepared a Fe-ZSM-S (1.78 Fe wt%) and Fe-S-1 catalysts (O.54+1.76 Fe wt%) with iron originally introduced in the MFI framework by isomorphous substitution during the synthesis. The samples have been characterized by porosimetry, DRS, powder X-ray diffraction (XRPD) and 57 Fe Móssbauer spectroscopy. It is found that FexOy nanoclusters are formed inside the S-1 zeolite by gradual migration of iron initially located in the framework tetrahedral site of the zeolite structure. Microporosity and XRPD results suggest that, even if the iron content is increased in the S-1 matrix, no large FexOy particles are formed. On the other hand, for the Fe-ZSM-5 sample the oxo-iron clusters have a higher nuclearity and they are still present inside the zeolitic channels. The catalytic data for the N2O decomposition indicate that the activity of the Fe-S-1 samples is affected by the nuclearity of the FexOy nanoclusters, with a beneficial influence of aluminum for the Fe-ZSM-S sample. [1] G. I. Panov, Cattech. 4, 18 (2000). [2] G. Berlier, G. Ricchiardi, S. Bordiga and A. Zecchina, J. Catal. 229, 127 (2005). [3] F, Kapteijn, G. Marban, J. Rodriguez-Mirasol and J.A. Moulijn, J. Catal. 167,256 (1997) [4] G. Fierro, G. Ferraris, M. lnversi, M. Lo Jacono and G. Moretti, Studies in Surf. Sci. and Catal. 135, 4964 (2001).

An extensive study of natural and synthetic Fe-bearing sphalerites (Fe-content ranging from 0.005 afu to 0.250 afu) has been carried out through the combined investigations of the temperature dependence of the magnetic susceptibility and of the 57Fe Mössbauer spectroscopic features. Magnetic susceptibility measurements evidence, in the low temperature regime, the presence of clustered Fe even in the most diluted samples, whereas all the Mössbauer spectra are described in terms of variable proportions of three components, namely one single and two doublets absorption, centred at the same isomer shift, relative to Fe ions and to different Fe clusters, respectively. The comparison of all the experimental results points out a self-affinity of Fe ions in sphalerite favoured by the superexchange interaction, which stabilises the formation of clusters even in diluted samples and may be related to both macroscopic inhomogeneous distribution and crystal zoning.

The spinel structure is based on a nearly ideal cubic close-packed array of oxygen atoms with tetrahedral (T) and octahedral (M) cavities. In common 2-3 spinels, one eighth of the T sites and one half of the M sites are occupied by heterovalent cations A and B in the ratio AB2O4, where A = (Mg, Fe2+, Zn, Mn2+) and B = (Al, Fe3+, Cr3+). Commonly there exists octa-hedral-tetrahedral disorder of A and B cations depending on thermal history. Consequently, the crystal-chemistry of spinels is described by the general formula IV(A1-iBi)VI(AiB2-i)O4, where “i” refers to the inversion parameter. There are two ordered configurations stable at low tem-perature, one with i = 0 (normal spinel; e.g., MgAl2O4, FeAl2O4, MgCr2O4, FeCr2O4) and one with i = 1 (inverse spinel; e.g. MgFe2O4, FeFe2O4). With increasing temperature disorder takes place, i.e. A and B cations undergo increasing intersite exchange over the three cation sites per formula unit. Modifications of T-O and M-O bond distances to accommodate various chemical compositions and/or cation distribution determine variations in the oxygen positional parameter u and the cell edge a0. Cr-bearing spinels can be found in different geological environments, usually related to mafic and ultramafic rocks from great depth in the mantle as inclusions in diamonds (Lenaz et al., 2009; Nestola et al., 2014) to extra-terrestrial material (Lenaz et al., 2015). In nature, several cations can enter into the structure originating a solid solution with a general formula (Mg, Fe2+)(Al, Cr)2O4. Other cations such as Fe3+ or Ti can be present in low amounts - although in some cases the Fe3+ content can be very high. It’s important to notice that almost all the major cations can move among the two sites apart from Cr that prefers the octahedral site. Given that, spinels with higher Cr content will show a limited possibility of inversion while those with high Mg and Al and low Cr could undergo different degrees of inversion. In order to see the effects of order/disorder phenomena via Raman spectroscopy we ana-lysed spinels already characterised by X-ray single crystal diffraction and electron microprobe, and many other spinels from the same suites characterised by electron microbe for a total of about 300 different natural Cr-bearing spinels with 0.03 < Cr < 1.68 atoms per formula unit. Preliminary data show that the relative intensities and shifts of the A1g peak can be related to the Cr/(Cr+Al) ratio, being at about 690 cm-1 and 745 cm-1for high and low Cr content, re-spectively. As far as concern the low Cr spinels, the Raman spectra of disordered spinels is characterised by a peak at about 162-166 cm-1 and a succession of smooth curves in the range 300-650 cm-1. Ordered low Cr-spinels do not show the peak at 162-166 cm-1 but a peak at about 404 cm-1 and two others not well developed peaks/curves in the range 600-650 cm-1.

Blue spinel from Luc Yen district in north Vietnam are included in marble. These marbles (and the associated spinel) come from the intense metamorphism, linked to successive oroge-nies, of an ancient carbonate platform from the Paleo-Tethys Ocean. Previous chemical and spectroscopic analyses (Chauviré et al. 2015) indicated that the blue color is due to cobalt (Co2+), with some iron contribution. Chemistry by LA-ICP-MS shows that the most intense blue spinels have about 13000 ppm Fe, 2500 ppm Ni, 1200 ppm Co, 1100 ppm Cr, while Ga, V, Ti and Mn are in the range 200-400 ppm. Chauviré et al. (2015) demonstrated through UV-Vis spectra that the main absorption band between 500 and 670 nm, the dominant origin of color in these blue spinels, is composed of a series of bands at approximately 545, 550, 560, 580, 590, and 625 nm. Bands at 545, 550, 580, and 625 nm are due to cobalt (Co2+) substituting for Mg2+ in tetrahedral sites of the spinel structure while the remaining absorption bands are allocated to iron (Fe2+) in tetrahedral sites of the spinel structure. Consequently, the spectra show transmission windows between 300 and 500 nm and between 700 and 900 nm that explain the blue color. As expected, the spectra show that iron (Fe2+) and cobalt (Co2+) are the main chromophore elements. Chromium makes a significant contribution to color if the concentration is above 1000 ppm. XRD single crystal analyses on several fragments show a cell edge of about 8.0864 Å and an oxygen positional parameter close to 0.2634. Some fragments were analysed through EPR spectroscopy, at X band (~9.5 GHz) and room temperature. A complex spectrum was obtained, in which two distinct features can be identified: a sextet at g~2.0, due to the hyperfine splitting, and ascribed to the Mn(II) ion. A second set of lines appear at g values in the range 1.6 and 2.0, whose variability as a function of the crystal orientation in the magnetic field point to an ion occurring in a medium-to-strong ligand field. Only Co(II) and Cr(III) can be proposed for the final attribution.