High temperature transformation of iron-bearing minerals in basalt: Mössbauer spectroscopy studies

The high temperature decomposition of basalt from Lower Silesia (Poland) was followed by Mössbauer spectroscopy investigation. The Fe content of the sample was ~9.0 at.%. The X-ray diffraction analysis shows that augite (37%) and olivine (12%) are major Fe-bearing mineral components. The sample also contains significant amount of anorthite (22%) and nepheline (17%). The sample was heated at various temperatures between 200o C and 1100o C for three hours. Up to a temperature of 500o C changes in contribution of Fe-bearing minerals are insignificant. Heating in the temperature range from 500o C to 1100o C leads to a systematic increase in contribution of iron oxides at the cost of contribution of silicate minerals, like augite and olivine. Mössbauer spectrum obtained after heating at 1100o C showed hematite as the main iron oxide phase. The ratio of Fe3+/Fetot in the non-heated sample was equal to 0.51 and after heating at 1100o C this ratio amounted to 0.89.