OH CONCENTRATIONS IN NATURAL TITANITES DETERMINED BY FTIR SPECTROSCOPY AND NUCLEAR-REACTION ANALYSIS

The OH content of titanite single crystals from different geological o ccurrences was studied by FTIR microspectroscopy and by nuclear reacti on analysis (NRA). Calibrating the OH absorption band at 3485 cm(-1) a gainst the OH content determined by NRA, the integral molar absorptivi ty epsilon(i) amounts to 67001 mole(-1) * cm(-2). The H2O contents o f the studied low-(Al,Fe) titanites range from 0.09 to 0.36 wt.%. The structural incorporation of OH is not correlated with the minor elemen t content. Variable OH concentrations of single crystals from alpine f issures indicate fluctuations of the activity of hydrous components du ring crystallization. Titanite can be regarded as an essential ''hydro us'' mineral phase of magmatic rocks.