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The extensive investigation carried out in recent years at the UNESCO site of Al-Khutm (Ibri, Oman) has allowed to uncover the monumental remains of a tower dated back to the third millennium BC and to collect an abundant ceramic assemblage from the associated soil deposits. Eighteen selected pottery samples have been investigated using a multi-analytical approach including microfocus X-ray computed tomography, X-ray diffraction, optical microscopy and prompt gamma activation analysis to analyse the vessel-forming technique and to characterise their micro-structure, mineralogical and chemical composition to recognise possible local vs. non-local raw materials. The results provided new insights on ancient manufacturing processes and revealed that most of the vessels were locally produced exploiting raw materials from the surroundings of the site with the exception of a fragment of a black slipped jar. The chemical results suggest that the latter was imported from the Indus area in nowadays Pakistan. This evidence integrates our knowledge about the presence of this type of vessels in Oman and confirms the involvement of inland centres like Bat and Al-Khutm into a large-scale exchange system.

Four samples of synthetic chromium-bearing spinels of (Mg, Fe 2+ )(Cr, Fe 3+ ) 2 O 4 composition and four samples of natural spinels of predominantly (Mg, Fe 2+ )(Al, Cr) 2 O 4 composition were studied at ambient conditions by means of optical absorption spectroscopy. Synthetic end-member MgCr 2 O 4 spinel was also studied at pressures up to ca. 10 GPa. In both synthetic and natural samples, chromium is present predominantly as octahedral Cr 3+ seen in the spectra as two broad intense absorption bands in the visible range caused by the electronic spin-allowed 4 A 2 g  →  4 T 2 g and 4 A 2 g  →  4 T 1 g transitions (U- and Y-band, respectively). A distinct doublet structure of the Y-band in both synthetic and natural spinels is related to trigonal distortion of the octahedral site in the spinel structure. A small, if any, splitting of the U-band can only be resolved at curve-fitting analysis. In all synthetic high-chromium spinels, a couple of relatively narrow and weak bands of the spin-allowed transitions 4 A 2 g  →  2 E g and 4 A 2 g  →  2 T 1 g of Cr 3+ , intensified by exchange-coupled interaction between Cr 3+ and Fe 3+ at neighboring octahedral sites of the structure, appear at ~14,400 and ~15,100 cm −1 . A vague broad band in the range from ca. 15,000 to 12,000 cm −1 in synthetic spinels is tentatively attributed to IV Cr 2+  +  VI Cr 3+  →  IV Cr 3+  +  VI Cr 2+ intervalence charge-transfer transition. Iron, mainly as octahedral Fe 3+ , causes intense high-energy absorption edge in near UV-range (ligand–metal charge-transfer O 2−  → Fe 3+ , Fe 2+ transitions). As tetrahedral Fe 2+ , it appears as a strong infrared absorption band at around 4,850 cm −1 caused by electronic spin-allowed 5 E  →  5 T 2 transitions of IV Fe 2+ . From the composition shift of the U-band in natural and synthetic MgCr 2 O 4 spinels, the coefficient of local structural relaxation around Cr 3+ in spinel MgAl 2 O 4 –MgCr 2 O 4 system was evaluated as ~0.56(4), one of the lowest among (Al, Cr)O 6 polyhedra known so far. The octahedral modulus of Cr 3+ in MgCr 2 O 4 , derived from pressure-induced shift of the U-band of Cr 3+ , is ~313 (50) GPa, which is nearly the same as in natural low-chromium Mg, Al-spinel reported by Langer et al. ( 1997 ). Calculated from the results of the curve-fitting analysis, the Racah parameter B of Cr 3+ in natural and synthetic MgCr 2 O 4 spinels indicates that Cr–O-bonding in octahedral sites of MgCr 2 O 4 has more covalent character than in the diluted natural samples. Within the uncertainty of determination in synthetic MgAl 2 O 4 spinel, B does not much depend on pressure.

Nineteen chromite crystals from the A, B, E, G, H, J and K chromitite layers of the Peridotite Zone of the Stillwater Complex (Montana, USA) have been studied by means of X-ray single crystal diffraction and microprobe analyses. The results show that samples from the basal A layer are quite different from the others showing very high oxygen positional parameter u (0.2633-0.2635) and Ti- contents (0.059-0.067apfu). Mg# values are within the range 0.21-0.23 while for the other chromites it is in the range 0.45-0.47. Moreover, for the other samples, according to the structural parameters, two groups have been identified. The first one comprises samples of layers B, E and G, the second includes H, J and K layer samples. It is supposed that high Fe2+ and Ti contents of A layer samples are due to the post-crystallization reaction with interstitial liquid. This fact allowed a very slow cooling rate as evidenced by the high u values. The fractionation of evolved magma from within the intrusion and pulse of a new magma bringing more chromium into the chamber lead to Cr- and Fe3+ -rich compositions and consequently to the increase of the cell edges. The decrease of u values seems to be related to the Cr+Fe3+ and/or Al contents.

A collection of polished stone axes from a late Neolithic site and an Early Bronze Age hill fort in South Tyrol (Italy) have been analysed through a multi-analytical approach, mainly based on non-destructive techniques (i.e. Raman spectroscopy, X-ray fluorescence and prompt gamma activation analysis) to identify the raw materials used in the same area during different periods and compare them with those in use in the surrounding territories. The analytical results suggest raw material exploitation strategies based on local or close sedimentary, metamorphic and magmatic rocks. Most of the artefacts are made from antigoritic serpentinite, whose origin is probably from Hohe Tauern (Austria) or related secondary deposits. These data confirm the importance of such raw material for the production of polished stone axes during recent prehistory and integrate the present knowledge about the distribution of antigoritic artefacts in north-eastern Italy and neighbouring countries.

For the first time, few detrital augite and pigeonite crystals have been found in the Eocene flysch basins of Istria (Trieste-Koper basin; Italy, Slovenia, Croatia) and Krk Island (Croatia). Their chemistry suggests that they are related to subalkaline rocks (within-plate tholeiites) crystallized at a pressure between 0 and 5 kbar. As a possible source, the nearby basaltic andesites of Ljubac have been taken into consideration. The argument for a ?Late Tertiary age of the Ljubac volcanics is that no detrital pyroxenes have been found in the Eocene flysch and Oligo-Miocene molasse deposits of the area (Lugovic et al., 1998). Radiometric data are not available until now. The detection of detrital pyroxene could be an indication of an older age of the Ljubac volcanics. The presence of similar pyroxenes in the Trieste-Koper and the Krk Island flysch and their absence in Brkini flysch suggest that the basin of Krk was linked with the Istrian basin rather than the Brkini basin.

Augite and diopside crystals from the Oligo-Miocene high-Mg and high-Al basalts, basaltic andesites and andesites of Montresta (Sardinia, Italy) have been analysed by means of X-ray single crystal diffraction and electron microprobe. It has been found that crystallization or equilibration processes took place within the crust at pressures below 5 kbar. In particular, samples from high-Al basalts, basaltic andesites and andesites crystallised at pressures below one kbar while those from high-Mg basalts crystallised in a range from about 1.5 to 4.5 kbar. The intracrystalline temperatures range between about 550 °C for high-Mg basalts and 750 °C for andesites. The M2[variant prime] site is occupied in each of the studied crystals, which implies slow cooling rates. [PUBLICATION ABSTRACT]

The influence on the structure of Fe2+ → Mg substitution was studied in synthetic single crystals belonging to the MgCr2O4–FeCr2O4 series produced by flux growth at 900–1200 °C in controlled atmosphere. Samples were analyzed by single-crystal X-ray diffraction, electron microprobe analyses, optical absorption-, infrared- and Mössbauer spectroscopy. The Mössbauer data show that iron occurs almost exclusively as IVFe2+. Only minor Fe3+ (<0.005 apfu) was observed in samples with very low total Fe. Optical absorption spectra show that chromium with few exceptions is present as a trivalent cation at the octahedral site. Additional absorption bands attributable to Cr2+ and Cr3+ at the tetrahedral site are evident in spectra of end-member magnesiochromite and solid-solution crystals with low ferrous contents. Structural parameters a0, u and T–O increase with chromite content, while the M–O bond distance remains nearly constant, with an average value equal to 1.995(1) Å corresponding to the Cr3+ octahedral bond distance. The ideal trend between cell parameter, T–O bond length and Fe2+ content (apfu) is described by the following linear relations: a0=8.3325(5) + 0.0443(8)Fe2+ (Å) and T–O=1.9645(6) + 0.033(1)Fe2+ (Å) Consequently, Fe2+ and Mg tetrahedral bond lengths are equal to 1.998(1) Å and 1.965(1) Å, respectively.

Detrital spinel is a widespread heavy mineral in sandstones from the Maastrichtian--Middle Eocene sedimentary basins in the SE Alps. Chemistry of detrital spinels from the Claut/Clauzetto and Julian Basins (N Italy and NW Slovenia) is used to constrain petrological and geochemical affinities and tectonic provenance of the source rocks.

In Late Cretaceous times, subduction of oceanic crust occurred to the north of the Adria plate and was followed by the formation of ophiolitic complexes. Continental collision in Alpine orogenic belts lasted from Late Cretaceous to Early Tertiary times. The progressive contraction of oceanic crust caused the uplift of previously rifted continental margin and platforms and the formation of foredeep flysch basins. Detrital Cr-spinels are widespread in Eocene sandstones of the Brkini, Istrian and Krk Island foredeep flysch basins. On the basis of their TiO2 content and FeO/Fe2O3 ratio, spinels derived from peridotites and mantle-derived magmatic rocks were distinguished. The first are statistically more abundant and are considered to have been derived from type I and II peridotites. The second appear to be mainly related to backarc basin products. These results suggest that Cr-spinels were derived from the erosion of the Internal Dinarides, where type II and III peridotites are present, and also from the Outer Dinarides, where type I peridotites crop out.