The 57 Fe nuclear forward scattering (NFS) of synchrotron radiation and the use of diamond anvils with helium as pressure medium allowed study of the electronic state of Fe (super 2+) in the chain silicate hedenbergite CaFeSi 2 O 6 at pressures up to 68 GPa. Characteristics of NFS time spectra were compared with those of conventional Mossbauer spectra. NFS time spectra of 57 Fe in hedenbergite revealed a reversible phase transition between 53 and 68 GPa at room temperature, which is probably a transition from the paramagnetic phase at low pressures to a magnetic phase at high pressures. If this interpretation is correct, the Neel temperature T N of hedenbergite depends critically on pressure (T N = 45 K at 1 atm).

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