Raman Confocal Microscopy of Minerals

Raman spectroscopy is commonly used for characterization in chemistry, because vibrational information is very specific for the chemical bonds in molecules. We use such an information  for studying behavior of chemical bonds and phase transitions under high pressure. Recently, we applied a relatively new technique, confocal Raman microscopy to study mineral distribution in meteorite RC 075. It was demonstrated confocal Raman spectroscopy  allowed us to study two-dimensional distribution of shock effects in meteorites, including high-pressure mineral phases in CH and CB chondrites, distribution of organics in meteorites, IDPs and cometary particles, distribution and identification of secondary minerals in Martian meteorites, and search for micron-sized grains of interest in polished sections and acid residues of meteorites (e.g., corundum, hibonite, SiC).

Reflected (a) and cross polarized transmitted (b) light images of RC 05: ol = olivine; pl = plagioclase; px = pyroxene. The optical image obtained in reflected and cross-polarized transmitted light (Fig. 1) reveals three minerals – olivine, pyroxene, and plagioclase. 

Raman spectrum taken inside the bright yellowish area of the polarized optical image is shown in below (Fig. a). The Raman spectrum has two distinct peaks centered at 855 and  823 cm-1 characteristic for olivine. Position and boundary of the olivine grain can be easily identified in a two-dimensional map of the Raman peak centered at 855 cm-1 (Fig. b).

Raman spectrum taken inside the bluish area in the optical imageis shown in a. It has two doublets centered at 663 , 685 and 1010, 1029 cm^-1 and characteristic to pyroxene structures, and can be identified as clinoenstatite. Spectrum of clinoenstatite is very close to that of orthoenstatite; the former, however, should have peaks at 430 and 581 cm^-1. The peak at 430 cm^-1 is hidden by a shoulder of the 417 cm^-1 peak, however, peak at 581 cm^-1 is seen in the Raman spectrum of the enstatite

Raman spectrum of the clinoenstatite (a) and map of the Raman peak centered at 1010 cm^-1 (b). The intensity of the 1010 cm^-1 peak is shown in a yellow color scale.

Recently we used Raman confocal microscopy for identification of the diamond-like BCx phases obtained under high pressure and high temperature conditions, to study titanomagnetite-magnetite series which serves as important magnetic carriers in paleomagnetic studies (Tatsumi-Petrochilos, et al. EOS Trans. AGU,89(52), GP31A-0791, 2008), and to investigate two stage serpentinization and magnetite formation in olivine-rich troctolite (Beard, Frost, Fryer. J. Petrol., in press, 2009).