Fire Dust: The sword part becomes super-heated, and can reach a maximum temperature of about 900°F
Wind Dust: The sword part can create a temporary mini-tornado to push his opponents back.
Water Dust: The gun part can fire a jet of water, this can either be used propulsion or to knock his opponents back.
Lightning Dust: The gun part, basically, for as long as their is lightning dust, becomes a shotgun/tesla gun combo.
Ice Dust: The gun part can freeze its enemies on contact the spread of the Dust.
Steam Dust: The sword releases this dust in powdered from, to create an explosive smokescreen in a 5X10 area (if you don't know why explosive read here: http://rwby.wikia.com/wiki/Dust#Crystalline_and_Powdered).
Gravity Dust: The sword creates a 0.001 second gravity well, which sucks all nearby entities into it within 20m radius.
Earth Dust: The gun hardens the crystal through the air overtime, making it even sharper on impact with its target.