Ricerc@Sapienza

A new, IMA-approved classification scheme for the spinel-supergroup minerals is here reported.

We study the effects of cation inversion x (Mg ↔ Al, with x representing the fraction of Mg and Al exchanged) and magnetic substitution (Mn → Mg) on the elastic properties of the MgAl2O4 spinel system using density functional theory and Brillouin scattering techniques. Our computations show that cation inversion decreases the molar volume of spinel and produces a stiffening of C11 and a softening of C12. Simulations and experiments agree within 2%. Density functional theory also captures the qualitative effect of Mg ↔ Al on C44, that is, an initial softening for inversion degree at x

Twenty natural spinel single crystals displaying colors almost representative for the entire spinel variability were investigated by electron microprobe and UV–VIS–NIR–MIR and FTIR spectroscopies. Eight of them, selected among the Fe-bearing ones, were also analyzed by X-ray diffraction, and five by Mössbauer spectroscopy to obtain information on the oxidation state and site distribution of Fe.

Diamonds and their inclusions are unique fragments of deep Earth, which provide rare samples from inaccessible portions of our planet. Inclusion-free diamonds cannot provide information on depth of formation, which could be crucial to understand how the carbon cycle operated in the past. Inclusions in diamonds, which remain uncorrupted over geological times, may instead provide direct records of deep Earth’s evolution.