In this paper, we present a systematic structural study on the (Al1-xGex)65Cu10+yMn25-y alloy system. The emphasis of the work is to understand the effect of Ge concentration on the occurrence, growth and morphology of the quasicrystalline phases in the system, as we move from Cu/Mn ratio of 20:15 to 10:25 in order to span the varied electronic behavior (as shown in the literature) of this quaternary system. Throughout the series, coexistence of icosahedral and decagonal phases has been observed. To the best of our knowledge, these are the first observations of their type in the alloy system (AlGe) CuMn. © 2002 Elsevier Science B.V. All rights reserved.