Clarification.

Some of the information in "Geologic Material as Physical Evidence" that appeared in the March 2004 issue requires clarification. On page 4, the author stated "Minerals, especially small-sized ones, commonly are identified using x-ray diffraction and spectrographic techniques. Other instruments of value to the forensic geologist exist, particularly the scanning electron microscope and the electron microscope." While x-ray diffraction is a useful tool in mineral identification, polarized light microscopy is the primary technique used by trained geologists in mineral identification. Forensic geologists in the FBI Laboratory have a number of other instrumental techniques at their disposal that they use on a limited basis for the identification of unknown inorganic materials. These include x-ray fluorescence spectroscopy, scanning electron microscopy with energy dispersive spectrometry, cathodoluminescence, and Fourier transform infrared spectroscopy.

Also, on page 4, the suggestion that soil samples be submitted in "only plastic locking bags or glass vials" is problematic. Glass tends to break during shipping, causing sample contamination. There also are many other appropriate sample containers that may be used for geologic evidence, the most preferable being those made of rigid plastic. Metal canisters never should be used. Additionally, on page 3, the author states the "... investigators should ensure that they remove earth materials from clothing ... with extreme care...." To guarantee the best preservation of geologic materials from clothing, the investigator should submit, if possible, the entire object to the FBI Laboratory, allowing the geologists to remove the materials themselves. This ensures the lab examiner the best chance for preservation of important structural information. For the most up-to-date information on submitting geologic samples, the investigator should refer to the Handbook of Forensic Services, revised in 2003 and available in both hard copy and online at: www.fbi.gov/hq/lab/handbook/intro.htm.