Spectroscopic Characteristics of Turquoise With Reddish-Brown Stripes From Shiyan, Hubei Province
KU Ya-lun1, YANG Ming-xing1, 2*, LIU Jia1
1. Gemmological Institute, China University of Geosciences (Wuhan), Wuhan 430074, China
2. Gem Testing Center, China University of Geosciences (Wuhan), Wuhan 430074, China
Abstract：Striped turquoise is a kind of popular variety in the turquoise market of Shiyan, Hubei Province. In this paper, a turquoise sample with the light blue-green substrate and reddish brown stripes was studied. Moreover, reddish brown stripes regularly distributed on the light blue-green turquoise substrate. It has been tested by microscopic observation, EDS, micro-laser Raman spectrometer and micro UV-VIS-NIR. The results show that reddish-brown stripes are formed by the regular gathering of nearly round hematite aggregation in turquoise. Hematite particles are fine and disseminated distributed in the form of dots and snowflakes in turquoise. The results of chemical composition test show that the iron content in the strip is higher than that in the substrate, and the FeOT content in the inclusion minerals is about 56.06%～59.13%. Micro UV-VIS-NIR spectra show the chromogenic ions in the inclusion minerals mainly are Fe3+. It can be seen that the weak absorption near 374nm is caused by the d-electron transition of Fe3+ (6A1→4E(4D)), the double absorption near 429 and 418 nm is caused by the d-electron transition of Fe3+ (6A1→4E, 4A1(4G)), and the weak absorption near 475 and 544 nm is caused by the electron transition of Fe3+ ([6A1+6A1→4T1(4G)+4T1(4G)]). The Raman spectrum of inclusion minerals is typical of hematite at 225，296，411，612，659，1 320 cm-1. The spectroscopic characteristics of inclusion minerals in striped turquoise indicate that the inclusion mineral is hematite. Hematite in the turquoise is the associated mineral in turquoise deposit. The existence of hematite in turquoise can provide data support for the origin identification of turquoise and the origin traceability of ancient turquoise. The periodic appearance of hematite, an inclusion mineral in the Striped turquoise, indicates the instability and periodicity of the formation environment of turquoise.
库雅伦，杨明星，刘 佳. 湖北十堰红褐色条纹绿松石的谱学特征[J]. 光谱学与光谱分析, 2020, 40(11): 3639-3643.
KU Ya-lun, YANG Ming-xing, LIU Jia. Spectroscopic Characteristics of Turquoise With Reddish-Brown Stripes From Shiyan, Hubei Province. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2020, 40(11): 3639-3643.
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