The main part of major element concentrations was measured at the Institute of Mineralogy of the University of Hannover using a Cameca SX100 electron microprobe operated through the Cameca PeakSight software. Additional data was generated at the Institute of Geosciences at Kiel University using a JOEL JXA 8900 R electron microprobe. Results from both labs have been cross-checked, analyzing identical samples. All elements have been measured at Kα emission lines with a focused and fixed beam, an acceleration voltage of 15 kV, a beam current of 15 nA, and a signal count time per element of 10s on peak and 5s on each background. Matrix-correction according to PAP. For each of the 39 samples, repetitive measurements on multiple crystals have been carried out. We put a strong focus on reliable primitive core measurements; nevertheless, for most samples, we also acquired data for rim compositions. P-values have been calculated based on a paired, two-sided t-test to evaluate the significance of the difference between core and rim mean concentrations statistically and allow for H0 hypothesis testing. Additionally, propagation of uncertainty has been calculated for Mg# and Ca#.