The AlMn system is very rich in phases with composition close to Al 4Mn. As solidification conditions change from very slow (casting) to extremely fast (atomized submicron-size droplets) the following phases will form: hexagonal μ phase ( a = 1.995nm; c = 2.452nm), hexagonal λ phase ( a = 2.841 nm; c = 1.238 nm), decagonal quasicrystal, icosahedral quasicrystal and microquasicrystalline or “amorphous” phase. In the present work, the potential interrelationship between the structures of the crystalline, quasicrystalline and amorphous Al 4Mn phases is investigated by a systematic study of electron diffraction intensities. Analysis of electron diffraction intensity modulations and their spatial relationships suggests that the phases have a structural skeleton of icosahedral units, possibly of the Mackay icosahedron type. Different crystalline and quasi-periodic phases can be formed by different stackings of the same icosahedral clusters and they are not necessarily in a single orientation. The amorphous structure can be described as a network of the randomly oriented clusters.