The chemical and phase compositions for heterogeneous materials are key to understanding their behavior. Specifically, for rock mineralogy, most investigations for obtaining mineral chemical and phase composition have relied on methods like optical petrography and electron microscopy. However, these methods primarily rely on using elemental compositions and stochiometric assumptions as a basis for identifying different minerals and thus cannot distinguish mineral polymorphs. Moreover, these techniques also require the use of thin sections which involve laborious and time-consuming sample preparations. Raman imaging is an alternative high-precision technique that allows direct fingerprinting of mineral polymorphs and can handle samples without extensive surface preparation. However, a majority of past Raman imaging investigations on mineral mapping rely on single Raman peaks to identify minerals and the subsequent phase maps that have been reported are often not definitive. To address these serious shortcomings, we report a novel Raman imaging protocol where we exploit characteristic peak intensity <i>ratios</i> instead of single peak intensities and demonstrate a superior analytical methodology for polymorph identification. Secondly, using image processing, we develop and report a novel phase map generation procedure that results in high-fidelity and high-resolution mineral phase maps. Collectively, these enhancements allow us to rapidly map an unpolished granite specimen (~ 2 x 2 mm) with an exceptionally high level of agreement (&gt;97%) and an extremely fine spatial resolution (&lt; 0.3 - 2 µm). These promising improvements in mineral and phase mapping, as demonstrated on various granites, can be extended to any heterogeneous, multi-phase system.

Rapid and accurate mineral mapping of granites using Raman imaging

ACS Fall 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.