Spectroscopic evidence for tetrahedrally-coordinated titanium in richteritic amphiboles

Anfiboli sintetici della serie richterite-Ti-richterite, esaminati in luce di sincrotrone tramite spettroscopia ďassorbimento dei raggi X, mostrano la sogliaK del Ti spostata verso le alte energie e separata in diverse componenti. Presentano inoltre una spiccata avansoglia. La posizione, ľunicité la forte intensità di questa avansoglia sono tutte caratteristiche del Ti4+ in coordinazione tetraedrica, a conferma di una debole banda addizionale osservata negli spettri IR. Synthetic amphiboles of the richterite-Ti-richterite series, when examined by X-ray absorption spectroscopy under synchrotron light, show their TiK edges shifted to high energies and splitted into several components. However, their most conspicuous feature is the strong pre-edge. Location, singularity, and intensity of such pre-edges are all typical features pointing out to Ti4+ in four-fold coordination, as it is also indicated by a weak new band occurring in the lattice vibration region of their IR spectra. Key words Titanium - Amphibole - Richterite - XANES - Synchrotron