ID-6-IN-1762 A Forensic Mineralogy Toolbox – the next generation of instrumentation for forensic applications

The examination of particles found in the environment, such as minerals, and particles found on a suspect or at a crime scene, such as gunshot residue (GSR) formed the basis of our search for better instrumentation to analyze these particles.

Minerals have traditionally been identified by the skilled mineralogist’s eye. The laboratory tools of XRF and XRD joined the instrumentation during the 20th century, as did the field tools of colorimetric spot tests and hand-held XRF devices. These tools work well for relatively common minerals and relatively large samples.

Over the past 20 years it has become possible to analyze crushed mineral material, as well as gunshot residue particles, using automated SEM and EDS systems. These processes are suitable for large-scale automatic analysis applications for both mineral liberation analysis (MLA) and gunshot residue analysis (GSR).

In the forensic sector, the analysis of a particular crystal or grain (and/or GSR particle) is often required because only small samples of material are available. The material is frequently millimeter or micron size, while GSR particles are often smaller. Since the 1960s it has been possible to characterize such samples using SEM/EDS/WDS. However these techniques do not work well with minerals with low concentrations of light elements such as Li, Be B, and .nH2O, or with the new heavy metal-free bullet primers (HMF).

With the advent of HMF, it is becoming more difficult to use basic SEM /EDS and GSR methods alone. Other techniques are required for the analysis of these types of ammunitions.

Consequently, a new, rapid method of mineral and inorganic particle classification has been explored using a toolbox of well-established techniques such as optical microscopy, SEM, EDS, Raman, CL and fluorescence. The SEM and optical systems, or the electron BSD signal, allow the user to find particles of interest, the EDS to determine their elements set, and the Raman to distinguish between polymorphs and to ratify non-detectable elements. All of these attachments have been mounted on the SEM. Figures 1 and 2 show an image/diagram of the combined system.

Properties such as color, density, laser-excited fluorescence and crystal morphology are among the experienced mineralogist’s tools. For this reason, an optical microscope is part of the system, not only to navigate but to allow color, fluorescence and morphology to be seen, both optically and with electrons.

Cases will be discussed that show application of these instruments to real samples, both in the mineral area and general physical evidence samples such as gunshot residue. The talk will also discuss the development and incorporation of new instrumentation on a SEM that will benefit and assist analysis for forensic applications.