NOVELTY - Forming (M1) nanostructured silicon involves: either a) combining a stoichiometric mixture of silicon tetraiodide and an alkaline earth metal silicide into a homogeneous powder, and b) initiating the reaction between the silicon tetraiodide and the alkaline earth metal silicide; or a1) grinding a stoichiometric mixture of silicon tetraiodide and an alkaline earth metal silicide into a homogeneous powder, and b1) reacting the silicon tetraiodide with the alkaline earth metal silicide.    USE - For forming nanostructured silicon and silicon-germanium (claimed) used for producing nanostructured silicon and silicon-germanium via solid state metathesis (SSM). The nanostructured silicon and silicon-germanium used for variety of applications such as thermoelectrics, photovoltaics, solar cell batteries and biological imaging.    ADVANTAGE - The method provides nanostructured silicon and nanostructured silicon-germanium having nanoparticles, nanopowders, nanoclusters, nanocrystals or nanowires morphology. The method is relatively inexpensive; does not require expensive equipment or toxic precursors; rapidly produces unfunctionalized nanostructured silicon and nanostructured silicon-germanium without the need for complex equipment; and is easily and efficiently scaled up from milligram quantities to gram scale reactions.    DETAILED DESCRIPTION - Forming (M1) nanostructured silicon involves: either a) combining a stoichiometric mixture of silicon tetraiodide (SiI4) and an alkaline earth metal silicide into a homogeneous powder, and b) initiating the reaction between the silicon tetraiodide and the alkaline earth metal silicide; or a1) grinding a stoichiometric mixture of silicon tetraiodide and an alkaline earth metal silicide into a homogeneous powder, and b1) reacting the silicon tetraiodide with the alkaline earth metal silicide; or a2) ball milling a mixture of silicon tetraiodide and an alkaline earth metal silicide into a homogeneous powder, and b2) reacting the silicon tetraiodide with the alkaline earth metal. An INDEPENDENT CLAIM is included for forming (M2) nanostructured silicon-germanium involving a3) combining a stoichiometric mixture of silicon tetraiodide and a germanium based precursor into a homogeneous powder, and b3) initiating the reaction between the silicon tetraiodide with the germanium based precursors.