Rapid, Reliable and Reviewable Mineral Identification with Infrared Microprobe Analysis

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Subject: LCSH



Forensic Science and Technology


Infrared microprobe analysis (IRMA) is a valuable technology for mineral identification. Prior to the discovery of X-ray diffraction, the polarised light microscope was the principal tool for identifying minerals. While X-ray diffraction and electron beam microanalysis made major contributions to mineralogy, IRMA contributes unique information about the chemistry of complex minerals. Using diamond internal reflection to collect infrared (IR) spectra of minerals is an approach that extends optical mineralogy to new levels. It is simple, direct and rapid. Traditional whole grain mounts or petrographic sections, used for polarized light microscopy, are analysed by IR internal reflection. Attenuated total reflection (ATR) spectra are collected by touching the diamond internal reflection element to areas of interest. Silicates, carbonates, nitrates, phosphates, hydrates and other minerals provide unique spectra for identification. Using the diamond ATR microscope objective allows for the selective isolation of individual minerals for simultaneous collection of microscopic, optical and IR data, thus enabling the indisputable identification of most minerals. Applying IRMA to forensic soil analysis is an example of using this IR spectral method. A library of diamond ATR spectra of common soil minerals was prepared. These reference data let the analyst confirm the identity of mineral grains in soil evidence. Polarised light microscopical examination is the primary step. Each phase is then characterized by its ATR spectrum and searched through the spectral library. IRMA unites light microscopy with IR spectroscopy to create a powerful system capable of identifying mineral grains and correlating microstructure with chemistry. This technique has great utility in the analysis of material in a forensic context, particularly in relation to trace evidence.


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Publisher Citation

Weinger, B., Reffner, J.A., De Forest, P.R. (2009). Rapid, Reliable and Reviewable Mineral Identification with Infrared Microprobe Analysis. In Ritz, K., Dawson, L., & Miller, D., eds. Criminal and Environmental Soil Forensics. Springer Netherlands. Pp. 431-443 ISBN: 978-1-4020-9203-9