Pretty much any powder will burn vigorously or explode if compressed or contained firmly. Apart from the obvious candidate of gunpowder, you can make bombs with custard powder or milk powder if you wanted to.
That's not what I meant fella...I'm a firefighter, so understand dust explosions etc....what I meant was, an unidentified powder. If I was that way inclined, it would be the easiest way of spreading a biological agent across the nations capital.
The powder is worrying....