Author name: John F. Rakovan

Raman spectroscopy is widely applied in metamorphic petrology and offers many opportunities for geological and tectonic research. Minimal sample preparation preserves sample integrity and microtextural information, while use with confocal microscopes allows spatial resolution down to the micrometer level. Raman spectroscopy clearly distinguishes mineral polymorphs, providing crucial constraints on metamorphic conditions, particularly ultrahigh-pressure conditions. Raman spectroscopy can also be used to monitor the structure of carbonaceous material in metamorphic rocks. Changes in structure are temperature-sensitive, so Raman spectroscopy of carbonaceous material is widely used for thermometry. Raman spectroscopy can also detect and quantify strain in micro-inclusions, offering new barometers that can be applied to understand metamorphic and tectonic processes without any assumptions about chemical equilibrium.

Geoscientists quickly recognized the broad applicability of Raman microprobe spectroscopy to the Earth and planetary sciences, especially after commercially built microprobe instruments became available in the early 1980s. Raman spectra are sensitive to even minor (chemical or structural) perturbations within chemical bonds in (even amorphous) solids, liquids, and gases and can, thus, help identify, characterize, and differentiate between individual minerals, fluid inclusions, glasses, carbonaceous materials, solid solution phases, strain in minerals, and dissolved species in multi-component solutions. The articles in this issue explore how Raman spectroscopy has deepened and broadened our understanding of geological and extraterrestrial materials and processes.