The data are magnesium (Mg) isotope composition, i.e. the relative difference of isotope ratios as defined in Coplen (2011, doi: 10.1002/rcm.5129). The reference was DSM-3 (see Galy et al., 2003, doi: 10.1039/b309273a) and data are given in per mil. Samples consisted of terrestrial peridotites and basalts as well as a suite of meteorites including chondrites, shergottites, diogenites and one angrite. A large portion of the data have been published in Hin et al. (2017, doi: 10.1038/nature23899).

Clay minerals (smectites) were synthesised experimentally to determine isotope fractionation factors (Li and Mg). The data are provided here. Interpretation is ongoing.

Paired water and river sediment samples were collected from Vietnam Australia, Cambodia and Nepal. Waters were analysed for major ions, Sr isotopes and Mg isotopes. Sediments were sequentially extracted using ammonium chloride, acetic acid and hydrochloric acid to target exchangeable ions, calcite and dolomite respectively. They were analysed for major ions and selected isotopes.