Gilalite Altered to Cuprite in Quartz
In 2004, gem-quality quartz that contained blue to green inclusions of the hydrated copper silicate mineral gilalite was found in Paraíba, Brazil. This material was sold as “Medusa quartz,” so named for the medusa phase of a jellyfish, which has an umbrella-like shape similar to these brightly colored inclusions. One specimen of this material contained an unusual red inclusion with the same umbrella shape (figure 1). This red inclusion revealed a surface-reaching crack. Microscopic examination showed a granular texture in the red areas. Raman analysis identified the red mineral as the copper oxide cuprite. It was apparent that the gilalite had been altered by secondary fluids that entered the crack. Neighboring gilalite inclusions were pristine and unaltered. The underside of the umbrella-like structure also revealed a blue ring, indicating that the inclusion had not completely altered (figure 2). The high-contrast blue and red colors seen in this particular sample of Medusa quartz make it a most intriguing inclusion specimen.
