Evolution of OH groups in diopside and feldspars with temperature
Yang, Yan; Xia, Qunke; Zhang, Peipei
European Journal of Mineralogy Volume 27 Number 2 (2015), p. 185 - 192
published: Mar 1, 2015
ArtNo. ESP147052702003, Price: 29.00 €
Using in situ FTIR and heating/cooling stage, we have investigated the temperature evolutions of OH bands in natural diopside, plagioclase and anorthoclase. The frequencies of three main resolved OH bands (3645, 3464 and 3361 cm–1 called band 1, 2 and 3, respectively) in diopside shift linearly with temperature. With increasing temperature, band 1 shifts to lower wavenumbers, band 2 exhibits almost no shift while band 3 shifts to higher wavenumbers. The integral absorbance of band 1, 2 and 3 decreases by 18.8, 10.1 and 31.4 %, respectively, from –50 to 400 °C. No simultaneous growth and decline of OH bands is observed during the whole process, excluding H proton transfer. In contrast to OH defects in diopside, the bands at lower frequencies in feldspars weaken while their bands at higher frequencies strengthen with increasing temperature, indicating H protons change positions in the crystal structure from one site with stronger H bond to another site with weaker H bond. These results reflect different local environments of OH defects and temperature dependent OH absorption coefficients in diopside, and change of H sites in feldspar structure with temperature. It provides important constraints on the microscopic mechanisms of hydrogen incorporation in these minerals.