Samples were collected with a Sigma-2 sampler (Waza et al., 2019) on the Caldeira rim of Fogo, Cape Verde, between 28 May 2008 and 08 June 2008. The geographical coordinates are N 14.9759°, W 24.3379°, height is approximately 1,630 m above sea level. Two samples were collected in parallel at the same location, termed 'A' and 'B'.Samples were subject to automated scanning electron microscopy with coupled X-ray analysis (Kandler et al., 2018).Each data file is one sample (approximately diurnal collection), an overview with meta data is given in the sample list file. Please refer to the description files for more details.