Fengruiite, [Ag ₆ Sb ₂ S ₇ ][Ag ₉ CuS ₂ Te ₂ ], a new Ag–Sb–Te sulfosalt mineral from the Haopinggou Ag–Pb–Zn–Au deposit, eastern Qinling, China

Fengruiite, ideally [Ag6Sb2S7][Ag9CuS2Te2], is a new mineral species of the pearceite–polybasite group discovered in the Haopinggou Ag–Pb–Zn–Au deposit, eastern Qinling, China, and approved by the IMA Commission on New Minerals, Nomenclature and Classification as IMA 2024-045. The mineral occurs as irregular grains (< 20 × 80 µm) intergrown with galena, cervelleite, and chalcopyrite in intermediate-sulfidation epithermal veins. Fengruiite is opaque, gray with a metallic luster, and brittle and has an estimated Mohs hardness of 3–4. EPMA analyses yield Ag (65.9 wt %–68.6 wt %), S (12.6 wt %–13.1 wt %), Sb (9.1 wt %–10.1 wt %), Te (6.3 wt %–7.6 wt %), and Cu (3.3 wt %–3.8 wt %), corresponding to the empirical formula [(Ag5.87Cu0.29)Σ6.16(Sb1.89As0.03)Σ1.92S7] [Ag9CuS2(Te1.28S0.63)S1.91]. Fengruiite is trigonal, space group P3‾m1 (#164), with a=7.6087(9) Å, c=11.970(2) Å, and V=600.13(17) Å3 (Z=1). Its structure consists of alternating negatively charged [Ag6Sb2S7] (A) and positively charged [Ag9CuS2Te2] (B) layers, characteristic of the polybasite-Tac polytype. The combination of a Te-dominant Te1/S1 site in the B-layer module and S-dominant anion sites throughout the A-layer module distinguishes fengruiite from Te-rich polybasite-Tac and benleonardite. As the first structurally characterized Te-rich member of the pearceite–polybasite group reported from the East Qinling metallogenic belt, fengruiite expands the known structural and chemical diversity of Ag sulfosalts and documents Te incorporation into an Ag-rich sulfosalt structure in an epithermal system.