Hydrothermal synthesis of ooliths.

The Y2O3-Fe2O3-H2O-CO2 system, in which the source of CO2 and H2O was HCO2H and the Y2O3/Fe2O3 ratio was 3:5, was studied in order to det. the hydrothermal conditions necessary for the formation of oolites and the mechanism of their formation. At 200° the formation of oolites isostructural with natural ancylite occurred, along with a stable carbonate phase, Y(OH)CO3, and an FeCO3 siderite phase. Below 200° Fe(HCO2)2.2H2O and Y(HCO2)3 and I±-Fe2O3 were the stable phases. At 780° YFeO3 and magnetite were the stable phases. The formation of the oolitic structure is explained by assuming that at low temps. CO is evolved from the HCO2H to form bubbles which become the active centers for pptn. and crystn. [on SciFinder(R)]