Determining the water content of nominally anhydrous minerals at the nanometre scale

The amount and distribution of water in nominally anhydrous minerals (NAMs) are usually determined by Fourier-transform infrared spectroscopy. This method is limited by the spot size of the beam to the study of samples with dimensions greater than a few micrometers. Here, we demonstrate the potential of using photoinduced force microscopy for the measurement of water in NAMs with samples sizes down to the nanometer scale with a study of water concentration across grain boundaries in forsterite. This development will enable the study of water speciation and diffusion in small-grained rock matrixes and allow a determination of the influence of nanoscale heterogeneity on the incorporation of water to NAMs.