This dataset contains major element geochemical data for magma plug rock samples ballistically ejected during vulcanian eruptions at three active volcanoes: Soufrière Hills Volcano (Montserrat, West Indies), Reventador Volcano (Ecuador), and Sangay Volcano (Ecuador). Concentrations of silicon (Si), aluminium (Al), calcium (Ca), magnesium (Mg), iron (Fe), titanium (Ti), potassium (K), sodium (Na), phosphorus (P), manganese (Mn), strontium (Sr), and barium (Ba) were determined using inductively coupled plasma optical emission spectrometry (ICP-OES). The samples were collected from the flanks of Soufrière Hills, Reventador and Sangay volcanoes. The dataset, in Microsoft Excel (.xlsx) format, include metadata describing individual samples, summarised major element results grouped by eruptive phase where applicable, and raw ICP-OES analytical data.