Interaction between different forms (fused and single crystal) of SiO2 with magnesium at 823 K for a relatively short times was studied revealing periodically arranged layers as a reaction product. These layers were composed of MgO of various morphology (fibres or particles) and Mg2Si phase. The reactive phase formation was still not a diffusion-controlled process, because of short annealing time, and it started not equally at the surface but in local centres. The reaction product bands cannot be treated as single-phase layers, but the presence of MgO and Mg2Si within the one type of layer and Mg2Si (crystalline or amorphous) within the other was evidenced.