gasinclusions

Gas inclusions are microscopic pockets of gas trapped within a mineral or rock during its formation or subsequent alteration, distinguishing them from liquid or solid inclusions. They occur in a variety of hosts including diamonds, quartz, olivine, calcite, and even ice; primary inclusions form with the host crystal, while secondary inclusions can form later along fractures or deformation zones.

Formation typically involves entrapment of gas from a vapor-rich melt or gas phase during crystallization; post-entrapment processes such as pressure changes or fracturing can also trap gas in newly formed cavities. Gas inclusions are valuable because they preserve snapshots of ambient gas compositions, pressures, and temperatures at the time of entrapment; in diamonds, mantle volatiles such as nitrogen, carbon dioxide, and methane are commonly studied. In ice and other materials, trapped gas or air bubbles can record past atmospheric composition and climate, serving as key data for paleoclimate reconstructions.

Analytical methods include polarized light microscopy for morphology, microthermometry to release gases, and spectroscopic techniques such as Raman and infrared spectroscopy, as well as mass spectrometry after sample crushing. These techniques help identify gas species and constrain physical conditions of entrapment.

Interpretation requires careful consideration of sealing and alteration effects, and uncertainties are tied to small sizes and potential gas loss during storage or processing. Gas inclusions thus provide a window into the history of minerals, materials, and environments, from deep Earth to past climates. See also inclusions in geology and paleoclimatology.