if you're at the point of exchanging materials for marks you're playing this game way too much. I play a couple hours every couple of days and have 21 legendaries, 12 exotics, half of both are fully upgraded, and i've never once exchanged mats for marks AND i feel like a crack addict with this game. And I've purchased the majority of those lengedaries, probably 15 of 21. Just slow the f down and go hit he treadmill or something to burn some energy