Mineralogical and Spectral Characteristics of Faustite from Sonora, Mexico
WANG Qing-nan1, DI Jing-ru1, 2*, HE Chong2, HE Bo3
1. Gemmological Institute, China University of Geosciences, Wuhan 430074, China
2. Gem Testing Center, China University of Geosciences, Wuhan 430074, China
3. Shenzhen Liansheng Jewelry Co., Ltd., Shenzhen 518020, China
Abstract：Faustite is rare and rarely mentioned in existing research and reporting. Mexico is an important producer of American turquoise, and Mexican turquoiseis active in the market recently. In this paper, the authors studiedthe chemical composition, phase composition, and a series of spectrum of turquoise samples from Mexico by conventional gemmological tests, X-ray fluorescence spectroscopy, X-ray powder diffraction, fourier transform infrared spectroscopy and UV-Vis spectroscopy, andpreliminarily discussed the deposit genesis. The results indicated that the main colors of Mexican turquoise are light blue and bluish white, and the features of pyrite with high degree of idiomorphic in matrix and surrounding rock and rare radial growth of dravite in surrounding rock were obviously different from turquoise in other origins. Mexican turquoise was recognized as Cu-bearing faustite due to the ratio of zinc oxide to copper oxide was greater than 1, which belongs to turquoise-faustite isomorphism series close to the end member mineral of faustite. And because of paragenesis with copper deposit, the content of CuO and ZnO in Mexican turquoise is much higher. The results of XRD experiment showed that the main mineral phase of Mexican turquoise is faustite, which is in agreement with the testing results of EDXRF testing, and the common mineral assemblage was faustite, quartz, orthoclase and dravite. The infrared spectrum was determined by the vibrationof hydroxyl (located at 3 400~3 700 cm-1), hydrated ion (located at 3 000~3 300 cm-1) and phosphate group (located at 1 000~1 200 and 400~650 cm-1 in fingerprint region) in the structure. And all the samples from Mexico showed the infrared absorption peak at 3 732 cm-1 while rarely seen in other origins, which has the function of indicatingthe originin a sense. Meanwhile, the integral computation within a range of 3 500~3 600 cm-1which related to constitution water with strongest hydrogen bonding can be used to determine the water content in the samples. Besides, the UV-Vis spectrumshowed that there were two peaks caused by O2--Fe3+ and Fe3+ at 256 and 430 nm, respectively. The band associated with the forbidden transition of Cu2+ at 670 nm was enveloped by the band formed by the electronic transition of Fe2+ at the center of 852 nm, finally, it was shown with the band centered on 800 nm which was caused by the combined action of Cu-Fe ions. Inferred from associated mineral combination, mineral structure and geological characteristics, Mexican turquoise is a nonmetallic mineral associated with porphyry copper deposit and belongs to the typical hydrothermal alteration genesis of intermediate-acid volcanic rocks.
王庆楠，狄敬如，何 翀，何 波. 墨西哥Sonora(索诺拉州)锌绿松石的矿物学及谱学特征[J]. 光谱学与光谱分析, 2019, 39(07): 2059-2066.
WANG Qing-nan, DI Jing-ru, HE Chong, HE Bo. Mineralogical and Spectral Characteristics of Faustite from Sonora, Mexico. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2019, 39(07): 2059-2066.
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