I highly recommend gentle heating as well as micro-spatulas...
Some chemicals are hydroscopic (They absorb water from the air around them), making them clump together and become difficult to measure and or make fine lines(for snorting)
All that is necessary is gentle heat applied to the outside of the bag left open (as simple as leaving it on top of your xbox for a couple of hours, or a therapeutic heating pad...) This makes it dry out, enabling you to get it as fine as possible.
All you can do to prevent such things is seal your goods properly. (Push all the air out around the substance and pinch the bag closed.)