INFRARED AND RAMAN MICROANALYSIS OF GEOLOGICAL SAMPLES

The important task of analyzing geological objects is usually one that involves the employment of an array of techniques including optical microscopy, x-ray diffraction (XRD), x-ray fluorescence (XRF), and scanning electron microscopy (SEM). Essentially, the task of characterization can be divided into two areas of interest; the physical properties of the sample and the chemical properties of the sample. Optical microscopy, XRD, XRF, and SEM yield information pertaining to the physical properties of the sample and IR and Raman provide complimentary chemical information. Spectroscopic analysis of geological samples has become more commonplace over the last several years and provides a very high degree of specificity with the ability to detect defects and inclusions. Raman spectroscopy is typically most useful for the investigation of inorganic molecules and probing structural differences in geological samples. Infrared spectroscopy is very useful for trace identification and quantification of species of interest. Area imaging for both Raman and infrared analysis is readily accomplished.

Several geological examples will be explored using traditional polarized light microscopy as well as infrared and Raman spectroscopy. The first example is the quantification of included gases in geological matter utilizing full-field infrared imaging. A baseline for doing the analysis allowed for absolute quantification of trapped water. A second example involved the detection of low concentrations of hydrocarbon and water inclusions in quartz also using infrared spectroscopic imaging. The last example involved the analysis of meteorites and the identification of components and their respective distribution using single point Raman microanalysis and area imaging. In each example, the identification of unknowns was readily accomplished by matching reference spectra to the unknown compounds.