Abstract

H/Si ionization in kornerupine, an (Mg, Al)-rich silicate mineral, has been investigated. There are significant variations (about 30% rel.) in the relative-to-Si ion yield for H [IY(H/Si)] as a function of chemical composition of the matrix kornerupine: ∼38–45 wt% Al₂O₃, ∼29–32 wt% SiO₂, ∼15–20 wt% MgO, ∼0–11 wt% FeO_tot, ∼2–4 wt% B₂O₃ and minor variations for the remaining components. There are strong correlations between IY(H/Si) and (Fe + Mn)(at) [where (at) represents the cation abundance in the sample (by atoms)] (r² = 0.80); for Mg and Al(at), r² = 0.73 and 0.90, respectively. The absolute ion yield for H [IY(H)] is strongly correlated with (Fe + Mn)- and Si(at) (r² = 0.92 and 0.94, respectively). It is possible to make adequate corrections to IY(H/Si) as a function of sample composition to obtain accurate H₂O (wt%) concentrations, reducing (if not overcoming) the need for specific standards (in most cases unavailable) that match the chemical composition of the sample. A model is proposed for H ionization in this matrix. The present outcome is qualitatively similar to the results obtained for other silicates (schorl, foitite, dravite, axinite, amphibole) and represents a valid basis for modelling SIMS ionization of H in silicates.