CO_2 Density-Raman Shift Relation Derived from Synthetic Inclusions in Fused Silica Capillaries and Its Application

The densities of CO₂ inclusions in minerals are commonly used to determine the crystallizing conditions of the host minerals. However, conventional microthermometry is difficult to apply for inclusions of small size (< 5–10 μm) or low density. Raman analysis is an alternative method for determining CO₂ density, provided that the CO₂ density–Raman shift relation is known. This study aims to establish this CO₂ density–Raman shift relation by using CO₂ inclusions synthesized in fused silica capillaries. By using this newly‐developed synthetic technique, we formed pure CO₂ inclusions, and their densities were determined by microthermometry. The Raman analysis showed that the relation between CO₂ density (D in g/cm³) and the separations (? in cm^?1) between the two main bands (i.e. Fermi diad bands) in CO₂ Raman spectra can be represented by a cubic equation: D (g/cm³)=0.74203(?0.019?³+5.90332?²–610.79472?+21050.30165)?3.54278 (r²=0.99920). Our calculated D value for a given ? is between those obtained from two previously‐reported equations, which were derived from different experimental methods. An example was given in this study to demonstrate that the densities of natural CO₂ inclusions that could not be derived from microthermometry could be determined by using our method.