Gemmological and Spectral Characteristics of Quartzite ("Dulong Yu")

In recent years, a new kind of jade named "Dulong Yu" has emerged in the jewelry market of Longling County, Yunnan Province.Due to the low production and late market entry, the market prospect is promising. However, there have been no academic research report on the gemmological and spectral characteristics of this gemstone. In this paper, the conventional gemmological instruments, polarizing microscope, X-ray powder diffractometer, infrared spectrometer, Raman spectrometer, X-ray fluorescence spectrometer, UV-visible fiber spectrometer were used to carry out detailed testing and analysis.The results showed that the main mineral components of the samples are α-quartz and sericite. The quartz has fine to medium grain crystallized structure, and the particle size is 0.1-1.4 mm, and the content is more than 90%. Sericite has microscopic scaly structure and remarkable recrystallization characteristics. The length of mica crystal is from 0.01-0.02 mm to 0.10-0.15 mm, and the content of mica crystal is 5%-10%. Occasionally, granulation zircon inclusions appear. X-ray powder diffraction analysis showed that it contained very small amounts of carbonate accessory minerals, including calcite, vaterite and fairchildite. X-ray fluorescence spectra and UV-Vis spectra showed that the body colour was caused by green sericite with filamentous and scales between quartz grains. Sericite was colored by Cr and Fe, and the absorption of⁴A₂→⁴T₂energy level transition in Cr³⁺ ions resulted in a 630 nm wide absorption band.The⁴A₂→⁴T₁ energy level transition absorption of Cr³⁺ ions and the charge transfer absorption between Fe²⁺-Fe³⁺ ion pairs combined to produce a 450 nm wide absorption band. And there is a positive correlation between the green depth and the content of element Cr and Fe.Infrared transmission spectra showed strong sharp absorption peaks at 2 853, 2 924, 2 956 cm^-1, and Raman spectra showed strong fluorescence background, which confirmed that the sample contained a small amount of paraffin and no resin glue.According to GB/T 16552-2017 Gems-Nomenclature, it should be named "Quartzite jade", and can be noted the market name "Dulong Yu" or "Aventurine quartz".