“…Ablating several clay-size minerals in one analysis have previously been done effectively using the same method to constrain fault reactivation histories in deep crystalline basements (Tillberg et al, 2020). In situ Rb-Sr dating of CRPG reference material Mica-MG (Govindaraju et al, 1994) prepared as a nano-powder pellet and a phlogopite mineral sample MDC sourced from the same quarry in Bekily, Madagascar were assumed to be of the same age (Armistead et al, 2020;Hogmalm et al, 2017;Li et al, 2020;Redaa et al, 2021) and were used as primary and secondary standards respectively. Furthermore, an independent illite pressed powdered pellet sample from Fithian, Illinois (Kralik, 1984) was also analyzed to determine whether the phlogopite nanopowder standard is suitable laser-ablation analysis of illite-rich granular shale samples.…”