Replacement degree of Al3+ and Cr/V ratio in high-V emeralds from Malipo, Yunnan, China

摘要

Replacement degree of the Al3+ and Cr/V ratio in emeralds from Malipo, Yunnan, China, was studied using infrared (IR) spectroscopy, X-ray diffraction (XRD), electron microprobe analysis (EMPA), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and ultraviolet-visible (UV-Vis) spectroscopy. The IR spectra of Malipo emerald samples indicated the presence of two types of H2O, types I and II, in the emeralds. The compositional results demonstrated that some Be2+ in the [BeO4] tetrahedron is replaced by Li+, and 7.15-12.35% of the Al3+ in the [AlO6] octahedron is replaced by Cr3+, V3+, Fe3+, Fe2+, Mg2+, Mn2+, Sc3+, Zn2+, Ti4+, and Ca2+. The diffraction data suggested that isomorphous substitution in Malipo emerald is mainly normal-octahedron type. LA-ICP-MS analysis indicated that the content of V3+ was an order of magnitude higher than that of Cr3+. Based on LA-ICP-MS, the Cr/V ratio of Malipo emerald was 0.039-0.162, categorizing the emerald as a high-vanadium type II emerald. The UV-Vis spectra demonstrated that the emerald color was primarily attributed to the interactions of Cr, V, and Fe, with V3+ contributing more than Cr3+. These unique characteristics distinguish the Malipo emeralds from emeralds of other provenance.