The new mineral mauriziodiniite IMA2019-036), NH4(As2O3)(2)I, was found at the Torrecillas mine, Iquique Province, Chile, where it is a secondary alteration phase associated with calcite, cuatrocapaite-(NH4), lavendulan, magnesiokoritnigite and torrecillasite on matrix consisting of native arsenic, arsenolite and pyrite. Mauriziodiniite occurs as hexagonal tablets up to similar to 300 mu m in diameter. Crystals are colourless and transparent, with pearly to adamantine lustre and white streak. The Mohs hardness is similar to 1. Tablets are sectile and easily flexible, but not elastic. Fracture is curved, irregular and stepped. Cleavage is perfect on {001}. The calculated density is 3.916 g/cm(3). Optically, mauriziodiniite is uniaxial (-) with omega = 2.07(calc) and epsilon = 1.770(5) (white light). The empirical formula, determined from electron microprobe analyses, is (NH4)(0.94)K-0(.03)(As2O3)(2)I0.92Cl0.03. Mauriziodiniite is hexagonal, P6/mmm, a = 5.289(2), c = 9.317(2) angstrom, V= 225.68(18) angstrom(3) and Z = 1. The structure, refined to R-1 = 4.16% for 135 I-o > 2 sigma I reflections, contains three types of layers: (1) a planar neutral As2O3 (arsenite) sheet; (2) an NH4+ layer that links adjacent arsenite sheets via bonds to their O atoms; and (3) an I- layer that links adjacent arsenite sheets via bonds to their As atoms. The layer sequence is I-As2O3-NH4-As2O3-I. Mauriziodiniite is isostructural with lucabindiite and is structurally related to gajardoite, cuatrocapaite-(NH4), cuatrocapaite-(K) and torrecillasite.