Correlated Petrographic Analysis

Abstract

This research reports applications of infrared and Raman spectroscopy to correlate microstructure, elemental composition and molecular structure of petrographic sections of rocks. Together, the combination of morphology, optical properties, elemental composition and molecular bonding provide a more complete analysis of a material, and increases our understanding of the processes of its formation and history. Henry Clifton Sorby took up the study of rocks and minerals using a polarized light microscope, and published an important memoir “On the Microscopical Structure of Crystals” in 1858 (Quart. Journ. Geol. Soc.). He pioneered petrography, the study of thin sections of rocks. Sorby also construction and use a micro-spectroscope to analyze the color of materials. Unknowingly, Sorby was the first scientist to practice correlated microscopy; combining microscopy and spectroscopy. Today, we are privileged to use photon and electron microscopes linked to a variety of spectrometers. Each spectrometer provides its unique information on the composition and structure of matter. The scanning electron microscope and microprobe, introduced over fifty years ago, correlate elemental composition with the microstructure of materials. This „element mapping‟ is now a routine technology; and is role in materials science is of prime importance. However, these technologies have limited ability when organic and molecular materials are analyzed. Infrared and Raman microprobes provide spectral data which provide details about the molecular structure on the microscopic scale. The unique advantages of molecular micro-spectroscopy are the ability to analyze hydrates, hydrogen-bonded water, and different states of covalent bonding in carbon, nitrates, phosphates, sulfates, silicates and numerous organic and inorganic materials. Polymorphic phases with identical elemental compositions have unique molecular spectra.