SANDS OF CRIME – AN APPLICATION OF PETROGRAPHIC METHODS TO FORENSIC TRACE EVIDENCE

A petrographic study of sand-grains found associated with human tissue (the evidence sample) in a discarded trash bag was undertaken in an attempt to locate the remains of a young Caucasian female, an alleged victim of organized crime. Law enforcement agencies collected twenty-nine samples of sand from area beaches. These samples were compared with the evidence sample by point-counting 400 grains of each sample for quartz (Q), feldspar (F), rock fragments (L), opaque minerals (O) and other minerals (N). The results of the counts were plotted first as a QFL diagram with ambiguous results. Since the purpose was comparison, not provenance and the evidence sample contained more than a total of 100 non-quartz grains the data was recalculated minus the Quartz component. Another plot of a smaller population of 13 samples, those which, like the evidence sample have more than 100 grains of F, L, O and N. Using these discriminants the evidence sample composed of 58% O + N, 22%L and 20%F compared well to two beach samples, one of which contained 56%O + N, 18% L, 26% F, and the other 57% O + N, 8%L, 35%F. A search of these two sites was inconclusive, however the construction of (ON)LF ternary plots for comparative purposes could be useful for future studies.