Feature Gems & Gemology, Winter 2010, Volume 46, No. 4

Update on Mexifire Synthetic Fire Opal

As a result of changes in the manufacturing process, recent production of the synthetic fire opal marketed as “Mexifire” exhibits some new properties. While the earlier material could be identified on the basis of low RI and SG values, the new synthetics have values that are quite similar to—and partially overlap those of—natural fire opals. With the change in the manufacturing process, the water content has also changed, as reflected in the IR spectra.