When you mine a crystal, you get an in-game message stating that the powder is activated. At this point, you can load the powder in a combat slot: one slot = 7 pcs. If you have mined a green crystal, then the powder acts as a very weak poison. Blue = a hit like a snowball, shuriken or any other proojectile weapon. Red = a temporary loss of life that is actually returned to the opponent after your hit (useful if the opponent is near death, possibly).