Acta Petrologica et Mineralogica

In recent years, a kind of black cyan nephrite containing pyrite has appeared in the domestic market. It is mainly produced in Xinjiang and belongs to a relatively rare nephrite variety, which has mining and utilization value. This article systematically analyzed the mineralogical and geochemical characteristics of seven samples using conventional gemological instruments, polarized light microscopy, infrared spectroscopy, Raman spectroscopy, X-ray powder diffraction (XRD), electron probe (EPMA) laser inductively coupled plasma mass spectrometry (LA-ICP-MS), and isotope mass spectrometer (MC-ICP-MS). The results show that the color of black cyan nephrite is dark green to black, the refractive index is 1.61, the relative density is 3.08~3.17, and the Mohs hardness is 6.0~6.5. The main component mineral is tremolite, the secondary mineral is mainly pyrite, and a small amount of chlorite, epidote, sphene, zircon, and graphite are also contained, with a typical fiber interlaced structure; The characteristic peaks of infrared and Raman spectra are consistent with the standard peaks of nephrite; The main chemical components of the sample are SiO₂, MgO, CaO and FeO. The Mg/(Mg+Fe²⁺) value indicates that some tremolite has transitioned to actinolite. Based on the trace element Cr-Ni mapping, the sample is identified as a dolomite marble type genesis, while the content of rare earth elements is relatively low, in a left leaning mode, The ore-forming hydrothermal fluid is mainly magmatic water, containing a small amount of metamorphic water. The sample contains pyrite with Co/Ni>1 and small amounts of As, Se, Cu, Zn and Pb, δ³⁴S ranges from 8.87‰ to 20.92‰, suggesting that it is of magmatic-hydrothermal origin and the source of sulfur is a mixture of magma and formation sulfur.

black cyan nephrite; pyrite; gemology and mineralogy; hydrogen-oxygen-sulfur isotope