THE HYDROUS COMPONENT IN ANDRADITE GARNET

Twenty-two andradite samples from a variety of geological environments and two synthetic hydroandradite samples were studied by Fourier tran sform IR spectroscopy. Their spectra show that H enters andradite in t he form of OH-. Amounts up to 6 wt% H2O occur in these samples; those from low-temperature formations contain the most OH-. Some features in the absorption spectra indicate the hydrogarnet substitution (SiO4)(4 -) <-> (O4H4)(4-) whereas others indicate additional types of OH- inco rporation. The complexity of the spectra due to multi-site distributio n of OH- increases with increasing complexity of the garnet compositio n.