In this project we developed a new geobarometer for mafic and ultramafic igneous rocks, which can be used by the scientific community for a wide range of mineralogical and petrological studies. The material here include the description of the geobarometer, guidelines for its use, software and chemical data acquired for some case studies.

These plagioclase and clinopyroxene mineral chemical and Sr isotope data come from Unit 10, Rum Layered Suite, NW Scotland. They underpin a publication entitled 'Rapid crystallisation of precious metal-mineralised layers in mafic magmatic systems', to be published in Nature Geoscience in 2020.

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).