2025/09/12 by Xiangping Gu, Xiangyang Shi, Hexiong Yang +1 · 1 voice
Chemistry · Earth and Planetary Sciences · Materials Science · #Crystal Structures and Properties #Geological and Geochemical Analysis #Radioactive element chemistry and processing
paper · pdf · doi:10.2138/am-2025-9910
openalex publication_date 2025/09/12 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
Abstract A new mineral species, wuyanzhiite, ideally Cu2S (IMA 2017–081), which is dimorphous with chalcocite, was discovered in the Bofang sandstone-type copper deposit, Hengyang, Hunan, China. It occurs as granular aggregates or oriented ribbons, 10 to >500 μm in size, composed of nanometric to micrometric anhedral crystals. Associated minerals include chalcocite, djurleite, digenite, sphalerite, tennantite-(Zn), bornite, pyrite, and smithsonite, with minor presence of uraninite, arsenic, zeunerite, and kasolite. Wuyanzhiite is opaque with dark gray color, metallic luster, and black streak, brittle with uneven fracture, and has a Mohs hardness of 3 and a calculated density of 5.618 g/cm3. Under reflected light, wuyanzhiite shows a gray blue color and becomes darker with increasing Fe content. The reflectance values (%) are 27.0–29.3 (470 nm), 23.8–26.6 (546 nm), 23.1–26.3 (589 nm), and 21.1–25.2 (650 nm). The empirical chemical formula from the average of 75 electron microprobe analyses is (Cu1.801+Cu0.0812+Fe0.0182+Ag0.001)Σ1.901S1.000 assuming charge balance with Fe2+. The chemical composition of wuyanzhiite exhibits a range of cation/S ratio from 1.993 to 1.710 and of Fe content from 0 to 2.88 wt% (0–0.074 apfu), with significant negative correlations between Cu (apfu), (Cu+Ag)/S and Fe (apfu), and a positive correlation between Cu2+ (apfu) and Fe (apfu). Wuyanzhiite is the tetragonal polymorph of Cu2S with space group P43212 and unit-cell parameters a = 4.0042(4) Å, c = 11.2555(13) Å, V = 180.47(3) Å3, and Z = 4. The structure of wuyanzhiite, refined to R1 = 0.0480 for 131 independent reflections [I > 2σ(I)], is characterized by approximate cubic close packing of S atoms along [0 1¯ 2] with an interlayer distance of 3.554 Å. Cu atoms are located at the centers of nearly equilateral triangles of S atoms with Cu-S bond lengths ranging from 2.296 to 2.317 Å, and the CuS3 triangles are corner-connected to form a framework with each S atom shared by six CuS3 triangles. The high-Fe content (>0.7 wt%) in wuyanzhiite may enhance its stability at ambient conditions. The name wuyanzhiite honors Yanzhi Wu (1931–2014) at Central South University, Changsha, China.