Fig. 4

Synchrotron µ-XRF/µ-XANES of samples 41 and 42. a False-colour μ-XRF maps of sample 41 (upper) and sample 42 (lower) used to select lazurite particles for μ-XANES (attenuated) spectral acquisition from the co-location of silicon (red), aluminum (green), and sulphur (blue); numbers refer to individual spectral acquisitions. Particles circled in white and labelled with uppercase letters correspond to spectra (solid curves) plotted in b, each as the average over the individual scans acquired for a given particle. The particle boxed in white corresponds to the uppermost spectrum (dotted curve) in b. b A selection of average normalised μ-XANES (attenuated) spectra each from single particles in sample 41 (upper, blue curves) and sample 42 (lower, black curves); the selection was chosen based on signal-to-noise. The uppercase letters correspond to lazurite particles circled in a from which the averages were taken, ranging from two to eight spectra for each. The uppermost curve (dotted blue) corresponds to a particle of gypsum, boxed in a