Thermoelectric p-type $Fe_{0.98}$ $Mn_{ 0.02}$$Si_2$ bulk specimens have been produced by mechanical alloying and consolidation by vacuum hot pressing. The subsequent isothermal annealing was not able to fully transform the mestastable as -milled powders into the $eta$ $-FeSi_2$ phase, so that the obtained matrix consisted of not only thermoelectric semiconducting $eta$-FeSi$_2$ but also some residual, untransformed metallic $alpha$ $- Fe_2$$Si_{ 5}$ and $varepsilon$-FeSi mixtures. Interestingly, $eta$ - $FeSi_2$ was more easily obtained in the low density specimen when compared to the high density specimen. The oxidation at 700 and $800^{circ}C$ in air led to the phase transformation of the above described iron - silicides and the formation of a thin silica surface layer.