Conjunctive use of quantitative and qualitative X-ray diffraction analysis of soils and rocks for forensic analysis

This paper describes a repeatability test, comparing conventional X-ray diffraction (XRD) analyses with the technique of quantitative X-ray diffraction (QXRD) as a determinant of mineral abundance. The conjunctive use of both methods allows specific mineral abundances to be matched between scene of crime (SOC) and suspects where soil or substrate mineralogy is similar. In our test, samples from potential SOC locations were taken from car tyre tracks. A car was driven to one location by an independent person and the car submitted for sampling. The tyre-tread sample showed potential correlation to two locations: one correct and the other incorrect. QXRD showed the mineral proportions of the tyre-tread sample matched only the correct location. However, QXRD did fail to discriminate two locations that XRD did show to be different. Both methods utilise the same sample and X-ray diffractogram, suggesting that their conjunctive use, preceded by standard Earth material forensic study, is recommended.