from personal experience (your mileage may vary), the powder was a bright yellow and looked like a very fine grained powder (think flour). the crystal on the other hand was dark and looked like sugar or salt crystals - big and odd shapes. still yellow, but darker and almost brown.
the powder takes like 3 days to hit you hard, and the crystal takes a few hours - for me 200mg of crystal in 2-3 hours felt the way 400mg crystal did after 3 days...
again, this was what I experienced, and others may have other experience - but crystal generally hits harder and faster.