Hydroxyl contents of accessory minerals in mantle eclogites and related rocks

Infrared spectra in the region 3000 to 3800 cm^(-1) have been measured on coesite, kyanite, sanidine, and rutile occurring in inclusions of eclogite, and on garnet and spinel in an inclusion of alkremite from South African kimberites. Coesite and sanidine contain virtually no H_2O or OH, although one sanidine crystal was observed to contain abundant H2O, apparently as fluid inclusions of molecular H2O. Kyanite contains significant OH, consistent with previous results for similar samples. Corundum gives no indication of the presence of H_2O or OH. Rutile containing significant amounts of Fe, Cr, Al, and Nb also contains significant amounts of structural OH. Garnet in alkremite contains small amounts of molecular H_2O, whereas the spinel coexisting with this garnet gives no indication of H_2O or OH, indicating that the spinel structure is not able to accommodate significant amounts of OH. Ammonium contents of all samples were less than the detection limit (about 10 ppm).