Transition-Metal Composition, Optical Absorption, and Channel-Water Characteristics of Natural V-Rich Beryl from the North Muzart River Area, Xinjiang, China.

Natural V-rich green beryl from the North Muzart River area, Xinjiang, was investigated using microscopy, EDXRF, UV-Vis-NIR, FTIR, and Raman spectroscopy. Ten specimens were examined microscopically; selected detached crystals were analyzed spectroscopically. Thirteen EDXRF analyses on seven detached crystals yielded V2O5- and Fe2O3-equivalent contents of 0.562-4.616 wt.% and 0.172-0.494 wt.%, respectively; Cr2O3 was not detected under the present analytical conditions, and normalized Fe2O3-V2O5-Cr2O3 compositions plot near the V2O5 endmember. Broad absorption bands near 429 and 617 nm fall within the spectral range commonly attributed to V3+ in beryl. Given the V-dominant EDXRF composition, these bands are interpreted as predominantly V-related; however, the V3+ assignment remains indirect because EDXRF does not determine the oxidation state, crystallographic site, or local coordination of V, and a minor contribution from Cr below the EDXRF detection capability cannot be excluded. Weaker responses near 366, 391, and 847 nm may involve Fe-related centers. Raman spectra from two selected green regions are consistent with the beryl host, and FTIR spectra of four selected crystals indicate predominantly type-II channel-water features with weaker type-I contributions. These samples provide a natural comparative system for evaluating V-related absorption in beryl and for comparison with V-doped synthetic beryl.