Comparison of X-ray diffraction patterns for samples in this study. Outcrop samples are denoted by their location and core samples as “C-depth below ground surface”. Sample “1-DGLS” is a core sample, but was collected from an unspecified depth. Additional information regarding these samples is found in Additional file 1: Table S1. (Left) Background-subtracted XRD spectra for samples in this study. Intensity was vertically scaled to display all samples simultaneously. (Right) Cluster dendrogram of XRD patterns. Clusters and linkage heights calculated via an average, unweighted distance algorithm. Intersample distances calculated as one minus the inter-sample Spearman’s \(\rho\) correlation coefficient over the \(2\theta\) range of 10°–45°.