This dataset contains mineral chemical data of primary and alteration phases in mafic rocks (basalt and diabase) from the Langseth Ridge and Afanasenkov Seamount, two volcanic centers on the ultraslow-spreading Gakkel Ridge, Arctic Ocean. The samples were collected during R/V Polarstern Expeditions PS78 and PS101 and USCGC HEALY Expedition HLY0102. Major elemental compositions were collected via electron microprobe. Details on the analytical procedure can be found in Albers et al. (2024).

Compositions of epidote with cations calculated on a basis of 12.5 O.