To correct for elemental and mass-dependent isotopic fractionation, reference materials (RM) with a well-known and homogeneous 87 Rb/ 86 Sr and 87 Sr/ 86 Sr distribution are applied. For in situ Rb-Sr dating, NIST 610 glass and MicaMg-NP are the most widely used. The latter is a finely ground pressed powder of phlogopite from a pyroxenite from southern Madagascar that displays a homogeneous age signal (519, 4 ± 6.5 Ma 9 ). Although these RM are frequently used in geochronological applications, none provides a proper matrix match to single-crystal mica, which is also the case for the recently tested fused mica mineral glasses. It has been shown that a lack of matrix match between RM and sample severely limits dating accuracy and systematic matrix age biases of as much as 10 % have been observed. We therefore produced secondary reference materials with well-known ages, determined by isotope dilution thermal ionization mass spectrometry (ID-TIMS) at GFZ Potsdam. The aim was to establish an additional set of mica reference materials with good matrix match to both natural K-white mica (Muscovite-phengite) and natural K-(Mg, Fe 2+ ) solid solution series (phlogopite-annite, 'biotite')