Farming tips: After a guild clear Ruins of Ahn'Qiraj, go in with a rogue, or druid, and stealth to the Silicate Feeders. They have drop rate around 15% and are easily soloed. After one dies move out of the "Cloud of Disease" and loot when the cloud is gone, you can kill around 35 per restart.
A skilled player with a good understanding of aggro zones can do this with any class, although it will be limited around 23 of Silicate Feeders per restart, you need stealth for max result.