Spectral Identification Characteristic of Nearly Black Tremolite-Nephrite("Heiqing") and Actinolite-Nephrite("Heibi")

"Heiqing" refers to dolomite-related nephrite with the colour of the nearly black, whose main mineral component is tremolite(tremolite-nephrite). "Heibi" refers to serpentinite-related nephrite with the colour of the nearly black, whose main mineral component is actinolite(actinolite-nephrite). In this paper, the chemical compositions and mineral components were tested by EPMA, LA-ICP-MS and XRD.The EPMA testing results show that the FeO_T content of "Heiqing" samples (2.21%-2.98%) is higher than that of "Heibi" samples (8.12%). Raman spectra show that the "Heiqing" samples reveal the standard tremolite absorption peaks, while the main peak positions of "Heibi" samples have several wavenumber deviations, moving in the direction of small wavenumber maybe caused by Fe content. According to the transmission test of micro-ultraviolet-visible spectrophotometer, it is found that there are absorption bands at 450, 680 nm of "Heiqing" samples at 400-800 nm, which attributed to the role of Fe. "Heibi" samples have 450 nm absorption bands and attributed to the role of Fe, and there are 660, 690 nm near a wide absorption band, which attributed to the role of Cr³⁺. The micro-ultraviolet-visible spectrophotometer testing results show "Heiqing" samples have absorption bands at 1 397, 1 915, 2 120, 2 130, 2 388, 2 465 nm, while "Heibi" samples have absorption bands at 1 400, 2 313, 1 394 nm. According to the literature, in nephrite the absorption of 1 390—1 420 nm is the synthesized peak of OH+H₂O, the strong absorption peak near 1 915 nm and the nearby weak absorption peak are the combined frequency of water molecule bending vibration and stretching vibration absorption peak, and 2 210—2 300 nm absorption attributed to the role of Fe-OH, 2 300—2 400 nm absorption attributed to the role of Mg-OH. The near-infrared spectroscopy transmission test results suggest that "Heiqing" samples have absorption peaks at : 5 224 cm^-1(1 915 nm), 4 738 cm^-1(2 120 nm), 4 349 cm^-1, 4317 cm^-1(2 310 nm), taking sample HQ-1 as an example."Heibi" samples have absorption peaks at 4 708 cm^-1(2 124 nm), 4 308 cm^-1(2 313 nm), 4 178 cm^-1(2 394 nm) taking sample No. MQ as an example. And the test results of near-infrared spectroscopy are consistent with the micro-ultraviolet-visible spectrophotometer.