Crystalline boron nanowires (BNWs) are grown on the entire surface of diamond powders by a solid-solid reaction approach. The as-grown BNWs have diameters in the range of 20-200 nm, lengths of several micrometers. High-resolution transmission electron microscopy (HRTEM) observation indicated the boron nanowires are composed of two structures, the interior of the nanowire is well crystalline in hexagonal structure and the surface of the nanowire is covered by a 5-10 nm thick tetragonal structure layer. Systematic analysis reveals that the conventional VLS (vapor-liquid-solid) growth model is not applicable to explain this kind of BNWs' growth mechanism. Hereby, an extended VLS model is proposed which can perfectly interpret the BNW's growth process on diamond surface and match experiment results very well. (C) 2014 Elsevier B.V. All rights reserved.