Photo by C Lloyd at SSERC (Public Domain)
This demonstration shows that, if finely divided enough, iron is actually reactive enough to react spontaneously with the air.
Iron II ethanedioate (iron II oxalate) decomposes on heating to give carbon dioxide, carbon monoxide, finely divided iron(II) oxide and iron. This can be done beforehand.
When sprinkled from a height this is oxidised rapidly and exothermically to iron(III) oxide giving a ‘sparkler’ effect. It is especially impressive in a darkened room.