X-RAY DIFFRACTION IDENTIFICATION OF GEOLOGIC TRACE EVIDENCE: IN THE CLASSROOM AND FOR THE COURTROOM
One of the analytical tools utilized by the students is x-ray diffraction (XRD), which is one of the most powerful tools available for identification of crystalline materials. Traditionally in geology, powder XRD would be used to identify the mineral components of a soil or ash layer and this information would be used perform such tasks as identifying economic mineral deposits or determining the sources of volcanic ash layers. However, XRD can also be used as a tool for identification and comparison of certain kinds of trace evidence, which is a general term for any small piece of physical evidence that links a suspect to a crime scene. Historically XRD has been little utilized due to the expense of the equipment and the expertise needed for interpretation, however improvements in technology and the existence of large reference libraries have made XRD a much more viable tool both for teaching and forensic use.
Students have been involved in projects such as XRD analysis of soil from a suspect's boot, which was compared to soils from a crime scene to determine if they were similar in nature or very different in nature. The same principles were used to analyze minerals used in building materials, paints, and cosmetics. For example, using XRD analysis of a lipstick smear, it is possible to identify the mineral components and potentially identify the manufacturer of the lipstick.