Abstract: The new mineral tooeleite occurs with pyrite, arsenopyrite, scorodite, and jarosite at the U.S. Mine, Tooele Country, Utah. Analysis by electron microprobe gave Fe₂O₃ 43.56%, As₂O₅ 38.61%, SO₃ 7.24%, and H₂O by the Penfield method 9.80%. For this analysis, the suggested formula is Fe8−2x3+[(AS1−xSx)O4]6(OH)6.5H2O; x is about 0.2.

Crystals are orthorhombic, perhaps Pbcm or Pbc2₁, with a = 6.416, b 19.45, c = 8.941 Å. The strongest diffraction lines are [d in Å, (hkl), (I)] 9.75 (020) (10); 3.208 (200,132) (9); 3.047 (061,220) (5); 4.476 ({002) (4) and 2.680 (240,113) (4). The mineral is optically negative with a small 2V; α = 1.94, β = 2.05, γ = 2.06. Hardness = 3, D_meas = 4.23, D_calc = 4.15 g/cm³ for Z = 2.