The high temperature behavior of trace hydrous components in silicate minerals



Roger D. Aines and George R. Rossman
Division of Geological and Planetary Sciences
California Institute of Technology, Pasadena, CA


Abstract

We have studied the high temperature behavior of water and hydroxide in quartz, feldspar, topaz, zircon, muscovite, cordierite, and beryl using high temperature infrared spectroscopy.  We have directly observed processes such as dehydration and changes in hydrogen speciation. In some minerals trace hydroxyl and water speciation and properties at temperatures of geologic interest can be dramatically different from those at 25C. In muscivite, no changes in speciation occur prior to dehydration at 750C, whereas in topaz hydroxyl sites interconvert at 500C. In metamict zircon stongly hydrogen-bonded hydroxyl in preferentially lost from a continuum of sites during continuous dehydration occurring from    400 to 900C. There are only minor changes in the O-H region spectrum of natural quartz at the alpha-beta trnsition pont. In feldspar one type of moleuclar water is lost at ~200C, and at 600 to 800 a second water type converts irreversibly to a new hydrous species. Changes at high temperatures common to the infrared absroption bands of all minerals studies are: broadening, a shift to lower wavenumbers, and a slight decrease in integral intensity. Temperature coefficients fo the O-H stretching peak shifts range from 0 to -0.045 cm-1/C. Lattice modes also braoaden and shift to lower wavenumbers, typically with temperature coefficients of about -0.03 cm-1/C.

Temp depencence of topaz OH

Temperature dependence on the topaz OH bands in alpha-polarization as a function of Temperature.