Magnesium powders are used widely in reactive and energetic composite materials, such as pyrotechnic formulations, solid fuels and explosives, as a vital ignition source. However, magnesium powders are highly reactive with atmospheric oxygen and moisture, forming the inert magnesium oxide and hydroxide. These reactions limit their shelf life, decrease their potency and affects the overall stability of these materials. In order to increase their long-term stability, protective magnesium coatings are desired. In this work, a method for coating magnesium powders using tetramethylcyclotetrasiloxane (D-4(H)) through a vapor-solid interface reaction is described. This reaction requires no solvents, little material, and does not produce any corrosive byproducts. Coated powders demonstrate increased stability when exposed to elevated temperatures and high humidity conditions, with no oxidation of the magnesium observable. Despite improved stability, the coatings do not negatively impact ignition temperature and dynamics for magnesium powders.