Tephra deposits of unknown age, and/or occurring in distal sequences that lack stratigraphic markers, are commonly identified by their glass compositions and mineralogical assemblages. Recent studies of widespread rhyolitic tephra deposits from Okataina Volcanic Centre (OVC), New Zealand, reveal a hitherto unrecognised geochemical and mineralogical diversity within individual deposits, and sometimes between and within individual lapilli in these deposits. These variations, subtle in some units, can occur both vertically and laterally through a tephra deposit, and result from the sequential or simultaneous eruption of separate batches of rhyolitic magma. This process often includes mingling of magmas in the eruption conduits, as demonstrated by disequilibrium mineral assemblages in pumice clasts. Some eruption episodes (e.g., 36 cal ka Hauparu, 17.6 cal ka Rerewhakaaitu) have tapped two or more magmas simultaneously, while others (0.7 cal ka Kaharoa; 15.4 cal ka Rotorua) have tapped multiple magmas sequentially. Some tephra deposits display the sequential and/or simultaneous emissions of different magmas from multiple vents through temporal phases of the episode (5.5 cal ka Whakatane). The resulting deposits can also show variations between different azimuths around the vent due to changes of wind direction during the episode. The internal heterogeneity in OVC tephra deposits was only recognised after comprehensive sampling through their thick proximal pyroclastic sequences and associated lavas. The internal heterogeneity highlights the inadequacy of fingerprinting tephra deposits from a small number of samples of restricted dispersal. Magma mingling at a single-clast-scale also has implications for geochronological techniques that use accessory phases (U-series) and/or require uniform melt geochemistry (fission-track on glass).