The Brittle Revenants in Storm Peaks respawn in less than a minute and there are a poop-load of them running around that frozen pond east of the Sons of Hodir camp. So by the time you make a circuit, the first few have already respawned. Unless you AOE them all, then you have to wait a few minutes. Not to mention, you can mine the corpses that non-miners leave.
BONUS: If you're a miner, you can almost double the amount of Earths you get from them.
Between kill drops and mining the corpse, I scored about 50 in an hour.
I searched "brittle revenant" and "Crystalized Earth" and didn't see any posts, so hopefully this isn't a repost.