The results of their refinement are summarised in Table . As it can be seen, the as-delivered commercial MgH2 contains tetragonal rutile-type -modification of magnesium hydride as a major phase, with the impurity (~9 wt.%) of metallic magnesium. Both phases are wellcrystallised that is testified by intensive and narrow peaks observed in the pattern (Figure (a)). Conversely, magnesium hydride prepared by ball milling of Mg powder in hydrogen has much less intensive and wider peaks (Figure ). Estimated from the peak broadening (LX profile parameter) crystallite size of the constituent phases, -MgH2 and metastable orthorhombic -MgH2 which was shown to be formed when applying high hydrostatic pressures or high-energy ball milling , was about 10 nm (see Table ). Adding of GLM and Ni/GLM, which was found to increase the rate of MgH2 formation during ball milling of Mg in H2 in 1.5-2 times, does not significantly change the XRD pattern but results in the increased noise/signal ratio particularly pronounced for MgH2-GLM composite (Figure )). Intensity Interesting that the ball milled MgH2-GLM composite does not contain the impurity of nanocrystalline MgO observed in MgH2 prepared by ball milling of Mg in hydrogen (see Table ) and presumably formed during oxidation of the fine powder of magnesium hydride during sample handling and the XRD measurements. Possible reason for that is in the enveloping of MgH2 particles with the GLM thus protecting their surface against oxidation. Introduction of the Ni catalysts results in the re-appearance of nanocrystalline MgO but in much smaller amount than for MgH2 prepared by ball milling of Mg in H2 (see Table ).