Dirty Deeds: Forensic Soil Provenancing Using X-ray Diffraction and Objective Colorimetry

Introduction: Forensic geology employs geoscience methods to answer questions in criminal investigations. Modern techniques often lack research establishing their validity. Objective: In this study, I attempted to determine the provenance of two unknown soil samples using objective colorimetry and X-ray diffraction. Methods: Two blinded samples were collected from two separate locations (disc golf course (DGC) and rock garden (RG)). I systematically sampled both locations and measured and compared objective colorimetry and X-ray diffraction (XRD) of the blinded samples and the systematic samples. I also performed Rietveld refinement on the XRD data. Results: DGC DeltaE ranged from 0.70 to 11.60 for Sample A (mean (SD): 3.33 (2.66)) and 0.27 to 14.34 for Sample B (mean (SD): 4.96 (3.34)). RG DeltaE ranged from 0.47 to 11.29 for Sample A (mean (SD): 4.99 (2.84)) and 3.34 to 16.46 for Sample B (mean(SD): 9.99 (3.14). Sums of squared differences (SSD) for XRD data from DGC ranged from 74.0 to 513.5 for Sample A (mean(SD): 295.3 (163.6) and 61.7 to 508.5 for Sample B (mean(SD): 298.5 (159.8)). SSD between Sample A and B was 67.3. Visual comparison showed similar peak distribution in Sample A, B, and DGC. Conclusion: I was unable to determine the provenance of either Sample A or B using colorimetry and XRD. These methods should be validated with further research before use in criminal proceedings.