In situ mica Rb‐Sr geochronology lacks a diverse range of widely utilised reference materials. Here, we characterize and evaluate six natural mica reference materials to test their suitability for in situ Rb‐Sr geochronology, including one phlogopite (Mica‐Mg‐NP phlogopite), three biotite (Mica‐Fe biotite, Mount Dromedary biotite and La Posta biotite) and two muscovite candidates (Högsbo muscovite, WA1ms muscovite). For each of these reference materials, we evaluate chemical and microstructural heterogeneity and assess age and/or Rb‐Sr isotopic homogeneity through ⁴⁰ Ar/ ³⁹ Ar, solution Rb‐Sr and long‐term in situ LA‐ICP‐MS/MS Rb‐Sr geochronology. Mount Dromedary biotite (99.37 ± 0.20 Ma; 2 s , including all sources of uncertainty) and Mica‐Fe biotite (307.75 ± 0.80 Ma) are effective low and high Rb reference materials for pulse and analogue collector modes on single‐collector systems, respectively, combining a wide spread of Rb/Sr ratios within and between grains, and producing accurate Rb‐Sr ages across multiple laser ablation sessions. La Posta biotite (91.30 ± 0.25 Ma) and Högsbo muscovite (1029.7 ± 2.0 Ma) are better suited as secondary low and high Rb reference materials due to minor chloritisation and alteration, respectively. Mica‐Mg‐NP phlogopite shows significant isotopic and age heterogeneity, outside of the precision of in situ Rb‐Sr geochronology, as well as showing different down‐hole fractionation compared with natural micas. WA1ms muscovite may prove a useful reference material, with a published ⁴⁰ Ar/ ³⁹ Ar age of 2613.3 ± 4.4 Ma, but further testing is required as its in situ Rb‐Sr age is significantly younger. All new reference materials investigated here are isochronous, rather than isotopically homogeneous, necessitating new data reduction schemes for processing isochronous data with accurate propagation of uncertainties and down‐hole fractionation corrections. The authors may be contacted to obtain vials of mica concentrates.