I believe that dust is a many-faceted form of matter.  Normally, it just contains power, which can be sapped by machinery (making it a fuel source) or combusted by application of force or energy (making it gunpowder or projectiles).  Different types of dust have different effects, naturally.  For a completely different project I have been working on a list of types of 'magic', which can also probably apply to dust as well.  If anyone's interested I can put the list here.

On another note, I've decided that four days for a contest is too long.  I'm reducing this one's deadline to Friday, one day from now, and future contests may be as little as two days long.