Читать книгу Encyclopedia of Glass Science, Technology, History, and Culture - Группа авторов - Страница 262

Iron is found in three redox states, Fe°, Fe²⁺, and Fe³⁺, but only the last two can enter the structure of silicate compositions in significant amounts. In this environment, the proportions of Fe²⁺ and Fe³⁺ vary with bulk chemical composition of glasses and melts, temperature, pressure, and redox conditions during equilibration of precursor melt. In magmatic liquids, the Fe³⁺/∑Fe ranges from essentially 0 to 1 (Figure 10) in such a way that this redox ratio has been employed to estimate the activity of oxygen and, therefore, oxygen budgets during formation and evolution of earth materials and, indeed, the Earth, itself.