OH concentration in natural titanites determined by FTIR spectroscopy and nuclear reaction analysis

The OH content of single crystals of titanites from 17 different geological occurrences was studied. On calibrating the OH absorption band at 3485 cm (super -1) against the OH content determined by nuclear reaction analysis, the integral molar absorptivity epsilon (sub 1) amounts to 67001 /mole/cm (super 2.) The H (sub 2) O contents of the low-(Al,Fe) titanites range from 0.09 to 0.36 wt.%. The structural incorporation of OH is not correlated with the minor element content. Variable OH concentrations in single crystals from Alpine fissures indicate fluctuations in the activity of hydrous components during crystallization. Titanite can be regarded as an essentially 'hydrous' mineral phase in magmatic rocks.