Hydrogen speciation and trace element contents of igneous, hydrothermal and metamorphic quartz from Norway

Abstract

Abstract Concentrations of a series of trace elements of 14 quartz samples from various geological settings (hydrothermal, igneous, metamorphic) in Norway were determined by LA-ICP-MS. FTIR spectroscopy was applied to the same quartz crystals in order to determine the H concentrations and the speciation of H in the quartz lattice. A refined hypothetical charge neutrality equation is suggested, where the atomic ratio of (Al3+ + Fe3+ + B3+) to (P5+ + H+ + Li+ + Na+ + K+) should correspond to 1 for natural quartz crystals. The determined concentrations of Al, Fe, B, P, Li, K and OH- species confirm approximately the charge neutrality equation. The high H/(Li+K+P) ion ratio of igneous quartz compared to hydrothermal and metamorphic quartz, suggests that igneous quartz preferentially incorporates H as OH- in lieu of Li, K and P. The results confirm that the FTIR absorption of the OH- band at 3595 cm-1 is attributed to structural B defects in the quartz lattice. The dominating H impurity in most of the quartz samples is, however, molecular H2O. The molecular H2O is presumably related to waterbearing micro pores and not to visible fluid inclusions, because the spectra were recorded from microscopically clear crystals.