The natural occurrence of OH in olivine

Gregory H. Miller, George R. Rossman
Division of Geological and Planetary Sciences
California Institute of Technology, Pasadena, CA  91125, USA

George E. Harlow
Department of Mineral Sciences
American Museum of Natural History
New York, NY 10024-5192


    Polarized IR spectra of olivine single crystals from 17 different localities show a tremendous variabilty in both mode and abundance of  hydroxide (OH) incorporation.  Kimberlitic olivines contain the most OH at an estimated concentration level of 976 H​/106 Si whereas olivines from basalts contain the least at 3 H​/106 Si.  Olivines of metamorphic and hydrothermal origin have  widely varying concentration levels between those of basalts and kimberlites. Over 30 distinct OH absorption bands have been identified. Most of these bands are not unique to individual localities but may be found in samples from several different localities. Pleochroism is consistent among localities, but relative band intensities vary. No evidence is found for molucular H2 in olivine.
    Hydrous minerals have been identified in olivine by their characteristic OH absorption bands.  Serpentine is commonly found and is clearly distinguishable from intrinsic OH.  Talc is present in only one sample. Prominent OH bands at 3572 and 3525 cm- ​1 are attributed to humite-​group minerals. 
    San Carlos, Arizona, olivines annealed in the presence of H2O, develop absorption bands which are found in natural samples; however, the OH absorption spectra of these annealed olivines are not identical to those of any single natural crystal.  Sharp-​band OH abundances in annealed samples are an order of magnitude lower than the max. measured in natural specimens.  The mechanical properties determined from these annealed olivines may not be directly applicable to mantle olivine because both the OH sites and concentrations are different.

Spectra of olivines from Zabargad Island polarized in the [100]
direction showing the variability observed for individual localities.