We could not find any information on the existence of rhombohedral BP in the literature, however, there is the experimental evidence for formation of rhombohedral polymorphic modification of zinc sulfide (ZnS) , the structural analogue of BP. This three-layer rhombohedral (3R) structure of ZnS was found to occur in the 600-1020C temperature range as an intermediate phase between sphalerite (3C) and wurtzite (2H) structures. In our case, the appearance of rhombohedral BP can be associated with deformation of as-formed sphalerite lattice in the course of ultrafast self-propagated high-temperature reaction, which leads to a change of interplanar distances for {111} 3С planes and, consequently, results in the change of the lattice symmetry.