The biogeochemical behavior of Fe and Al play an important role in several different reactions occurring in aqueous systems, soils, sediments and in the atmosphere. The chemistry of different crystalline oxyhydroxides and oxides of these two important elements, and their solution speciation is well studied in the past three decades. Despite their ubiquitous presence, the chemistry of amorphous and poorly crystalline oxyhydroxides of these two elements is poorly understood. These metastable phases persist in different environmental conditions for a longer time and influence the solubility and transport of different contaminants and nutrients in the environment. In addition, the associated counter and coions modify the occurrence and the reactivity of these phases. The recent synchrotron X-ray, infrared and NMR spectroscopy studies on Fe-, and Al-oxyhdyroxide systems revealed new information on the solution speciation and on the chemistry of these metastable precipitates. This talk will present a synopsis of these new findings.