Magnesium when hydrided has low thermal and electrical conductivity and carbon coating would be useful to remedy this for a variety of purposes. In this study, carbon coating was achieved by co-feeding magnesium and methane into a thermal plasma reactor. This yielded carbonaceous material with magnesium particles 5-10 nm in size embedded in graphitic matrix. A further reduction down to 2-3 nm was possible but required reductions in the precursor feed rate. 2 wt% carbon was sufficient to fully protect magnesium particles of approx. 260 nm in size. Light milling, however, disrupts the continuity of graphitic envelop and the particles then react both with oxygen and hydrogen. (C) 2017 Elsevier B.V. All rights reserved.