Abstract：Durango City, Mexico, is one of the richest sources of gem-quality fluorapatite. In previous studies, Mexican apatite was mainly used as a reference material for geochronology and mineralogy, with few gemological and spectroscopic materials. As a kind of natural luminescent material, early scholars mainly used laser-induced photoluminescence spectra to study apatite from unknown origin, but lacked 3D fluorescence spectra. In this paper, nine apatite samples from Durango City, Mexico, were systematically examined by using basic gemological tests, LA-ICP-MS chemical analysis, FTIR spectroscopy, Raman spectroscopy, UV-Vis-NIR absorption spectroscopy and 3D fluorescence spectroscopy, aiming to enrich thedata of spectrum of Mexican apatite and to provide the scientific information for origin determination. Chemical research shows apatite is rich in rare earth elements (REE), with high contents of La, Ce, Pr, Nd, and Sm, with average contents of 3 956, 5 430, 472, 1 596, and 213 μg·g-1, respectively, which shows the characteristics of obvious enrichment of light REE and deficit of heavy REE. The average value of δEu is 0.29, with significant Eu negative anomaly, and the Ca/P molar ratio is close to the standard value of 1.68 of magmatic apatite, which indicate that Mexican apatite is the product of magmatism and the forming magma is in a moderately reductive state. FTIR spectroscopy shows that the intensity of the absorption peaks at 606 and 575 cm-1 in the fingerprint region has obvious directionalregularity, which can provide a basis for crystal orientation. The functional group region shows absorption peaks of 3 482, 3 538, and 3 556 cm-1 of structure water. In the UV-Vis-NIR absorption spectrum, the single peak at 528 nm and the double peaks at 578 and 585 nm caused by Nd3+ generate the obvious transmission window in the yellow-green region. Therefore, it is speculated that Nd3+ causes the yellow-green color of apatite. In the UV region, the absorption peak at 298 nm is responsible for the absorption edge in the visible violet region, presumably caused by Ce3+. Studies on the 3D fluorescence spectrum showthe strongest fluorescence peak (λex300 nm/λem356 nm), caused by the electron leap of Ce3+. In addition, the emission peaks at 603 and 647 nm in the red region are caused by the electron leap of Pr3+ and Sm3+, corresponding to the dark red fluorescence phenomenon observed under the UV lamp. Therefore, the dark red fluorescence is presumed to be caused by Pr3+ and Sm3+. The systematic spectroscopic features in this study enrich the spectroscopic data of apatite of Mexico and provide a scientific basis for origin determination.
Key words：Mexico; Apatite; REE; UV-Vis-NIR spectrum; 3D fluorescence spectrum
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