Abstract: Leisingite, ideally Cu(Mg,Cu,Fe,Zn)₂Te⁶⁺O₆·6H₂O, is hexagonal, P3 (143), with unit-cell parameters refined from powder data: a = 5.305(1), c = 9.693(6) Å, V = 236.2(2) ų, c/a = 1.8271, Z = 1. The strongest six reflections of the X-ray powder-diffraction pattern [d in Å (I) (hkl)] are: 9.70 (100) (001), 4.834 (80) (002), 4.604 (60) (100), 2.655 (60) (110), 2.556 (70) (111) and 2.326 (70) (112). The mineral is found on the dumps of the Centennial Eureka mine, Juab County, Utah, U.S.A. where it occurs as isolated, or rarely as clusters of, hexagonal-shaped very thin plates or foliated masses in small vugs of crumbly to drusy white to colourless quartz. Associated minerals are jensenite, cesbronite and hematite. Individual crystals are subhedral to euhedral and average less than 0.1 mm in size. Cleavage {001} perfect. Forms are: {001} major; {100}, {110} minute. The mineral is transparent to somewhat translucent, pale yellow to pale orange-yellow, with a pale yellow streak and an uneven fracture. Leisingite is vitreous with a somewhat satiny to frosted appearance, brittle to somewhat flexible and nonfluorescent; H(Mohs) 3–4; D(calc.) 3.41 for the idealized formula; uniaxial negative, ω = 1.803(3), ɛ = 1.581 (calc.). Averaged electron-microprobe analyses yielded CuO 24.71, FeO 6.86, MgO 6.19, ZnO 0.45, TeO₃ 36.94, H₂O (calc.) [21.55], total [96.70] wt.%, leading to the empirical formula Cu1.00(Mg0.77Cu0.56Fe0.48Zn0.03)Σ1.84Te1.066+O6.02·5.98H2O based on O = 12. The infrared absorption spectrum shows definite bands for structural H₂O with an O-H stretching frequency centered at 3253 cm⁻¹ and a H-O-H flexing frequency centered at 1670 cm^−l. The mineral name honours Joseph F. Leising, Reno, Nevada, who helped collect the discovery specimens.