The reaction of lithium tetrahydridoborate and iron bromide in high boiling ether as reaction medium produces an ultrafine, pyrophoric and magnetic precipitate. X-ray and electron diffraction proved the product to be amorphous. According to Xray absorption fine structure spectroscopy (XAFS) the precipitate has FeB structure up to nearly two coordination spheres around an iron absorber atom. Transmission electron microscopy (TEM) confirms the ultrafine powder to be nanoscale. Subsequent annealing at 450 degrees C causes the atoms to arrange in a more distinct FeB structure, and further thermal treatment to 1050 degrees C extends the local structure to the alpha-modification of FeB. Between 1050 degrees C and 1500 degrees C alpha-FeB is transformed into beta-FeB.