ИСТИНА

Fayalite is the end-member compound of olivine — the most abundant mineral in the upper Earth mantle. Studies on the pressure-induced phase transformations in olivine play a key role in understanding the processes occurring in this part of the Earth interior. Investigating the interaction of olivine with gases at high pressure is of no less importance because the Earth crust and upper mantle contain lots of various gases, too. As the starting material, we used the fayalite powder synthesized by solid-state reaction of silica, carbonyl iron and hematite at T = 1000 °C in the reduced atmosphere. Powder samples were then exposed to an H2 atmosphere at P = 7.5 GPa and T = 280 °C for 24 hours, quenched to −196 °C to prevent hydrogen losses after the pressure release and further studied in the quenched state at ambient pressure and T = 85 K by x-ray diffraction and Raman spectroscopy. According to these studies, the hydrogenated samples of fayalite completely decomposed to a mixture of iron hydride with a double-hcp crystal structure and coesite, a high-pressure phase of silica.