Arsenoústalečite is a new mineral discovered in a sample collected from the abandoned Ústaleč deposit near Horažďovice, SW Bohemia, Czech Republic. It occurs as rare anhedral grains, up to 40 μm in size, in a calcite gangue, associated with stibioústalečite, hakite-(Hg), berzelianite and uraninite. Arsenoústalečite is dark grey, with a metallic lustre. Mohs hardness is ca. 3½–4; calculated density is 5.730 g/cm3. In reflected light, arsenoústalečite is pale grey with a yellowish shade; it is isotropic. Internal reflections were not observed. Reflectance values for the four COM wavelengths in air [R (%) λ (nm)] are: 33.3 (470); 33.1 (546); 33.0 (589); and 32.9 (650). The empirical formula of arsenoústalečite is (Cu5.81Ag0.17)Σ5.98(Cu5.95Fe0.02Zn0.02Hg0.01)Σ6.00(As1.40Sb0.87Te1.73)Σ4.00(Se10.30S2.32)Σ12.61. The ideal formula is Cu12(As2Te2)Se13, which requires (in wt.%) Cu 34.76, As 6.83, Te 11.63, Se 46.78, total 100.00. Arsenoústalečite is cubic, I$\bar{4}$3m, with unit-cell parameters a = 10.6580(19) Å, V = 1210.7(6) Å3 and Z = 2. The strongest reflections of the calculated powder X-ray diffraction pattern [d, Å (I, %) hkl] are: 3.077 (100) 222, 2.848 (10) 321, 1.946 (12) 521, 1.884(52) 440 and 1.608(21) 622. According to the single-crystal X-ray diffraction data (R1 = 0.0285 on the basis of 334 unique reflections with Fo > 4σFo and 24 refined parameters), arsenoústalečite is isotypic with other tetrahedrite-group minerals. The crystal structure of co-existing stibioústalečite, with an empirical formula of (Cu5.69Ag0.07)Σ5.76(Cu5.80Zn0.13Fe0.06Hg0.01)Σ6.00(Sb1.82As0.42Te1.76)Σ4.00(Se9.52S3.10)Σ12.62 and unit-cell parameters a = 10.6975(16) Å, V = 1224.2(5) Å3 and Z = 2, was refined to R1 = 0.0191 on the basis of 267 unique reflections with Fo > 4σFo and 24 refined parameters. Structural relationships and crystal-chemistry of both members of the ústalečite series are discussed. Arsenoústalečite is named after its type locality, the Ústaleč deposit and its chemical composition. The mineral and its name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA2022-116).

Arsenoústalečite 是一种新矿物，是在捷克共和国波希米亚西南部霍拉佐维采附近废弃的 Ústaleč 矿床中采集的样本中发现的。它以稀有的反角晶粒形式出现，大小可达 40 μm，存在于方解石脉石中，与锑长石、绿铜长石 (Hg)、绿菱石和铀长石相关。 Arsenoústalečite 呈深灰色，具有金属光泽。莫氏硬度约为. 3½–4；计算密度为5.730 g/cm 3。在反射光下，arsenoústalečite 呈浅灰色并带有淡黄色色调；它是各向同性的。没有观察到内部反射。空气中四个 COM 波长的反射率值 [ R (%) λ (nm)] 为：33.3 (470)； 33.1（546）； 33.0 (589)；和 32.9 (650)。砷老铁矿的经验公式为 (Cu 5.81 Ag 0.17 ) Σ5.98 (Cu 5.95 Fe 0.02 Zn 0.02 Hg 0.01 ) Σ6.00 (As 1.40 Sb 0.87 Te 1.73 ) Σ4.00 (Se 10.30 S 2.32 ) Σ12.61。理想的分子式为Cu 12 (As 2 Te 2 )Se 13，其需要(重量％)Cu 34.76、As 6.83、Te 11.63、Se 46.78，总计100.00。 Arsenoústalečite 是立方体，I $\bar{4}$ 3 m，晶胞参数a = 10.6580(19) Å, V = 1210.7(6) Å 3和Z = 2。计算得出的粉末 X- 的最强反射射线衍射图[ d , Å ( I , %) hkl ]分别为：3.077 (100) 222、2.848 (10) 321、1.946 (12) 521、1.884(52) 440 和 1.608(21) 622。 -晶体X射线衍射数据（R 1 = 0.0285，基于F o > 4σ F o的334次独特反射和24个精炼参数），砷古石与其他四面体族矿物是同型的。共存辉石的晶体结构，经验式为 (Cu 5.69 Ag 0.07 ) Σ5.76 (Cu 5.80 Zn 0.13 Fe 0.06 Hg 0.01 ) Σ6.00 (Sb 1.82 As 0.42 Te 1.76 ) Σ4.00 (Se 9.52 S 3.10 ) Σ12.62和晶胞参数a = 10.6975(16) Å、V = 1224.2(5) Å 3和Z = 2，基于F o > 4σ F o的 267 次唯一反射和 24 个细化参数，细化为R 1 = 0.0191。讨论了 ústalečite 系列两个成员的结构关系和晶体化学。 Arsenoústalečite 以其类型产地、乌斯塔莱奇矿床及其化学成分命名。该矿物及其名称已获得国际矿物学协会新矿物、命名和分类委员会的批准 (IMA2022-116)。