Silicon-based nanowires have been grown from commercial silicon powders under conditions with different oxygen and carbon activities. Nanowires grown in the presence of carbon sources consisted of a crystalline SiC core with an amorphous SiO x shell. The thickness of the SiO x shell decreased as the oxygen concentration in the precursor gases decreased. Nanowires grown in a carbon-free environment consisted of amorphous silicon oxide with a typical composition of SiO1.8. The growth rate of nanowires decreased with decreasing oxygen content in the precursor gases. SiO1.8 nanowires exhibited an initial discharge capacity of ∼1300mAhg−1 and better stability than those of silicon powders. A vapor-induced solid–liquid–solid (VI-SLS) mechanism is proposed to explain the nanowire growth (including silicon and other metal-based nanowires) from powder sources. In this approach, both a gas source and a solid-powder source are required for nanowire growth. This mechanism is consistent with experimental observations and also can be used to guide the design and growth of other nanowires.