Primal Sargerite is a new crafting material of Patch 7.3, which binds when picked up.
There are a lot of usage for Primal Sargerite. Nearly all of the professions will use it. They are replaced with Blood of Sargeras before Patch 7.3.
Meanwhile, Primal Sargerite is also the main material for compounding the Primal Obliterum. New crafted Gears will be upgraded to ilvl935 by Primal Obliterum and Primal Sargerite.
How to farm Primal Sargerite?
1. Transmutes 25 Blood of Sargeras into 1 Primal Sargerite. 1 day cool down. Requires Alchemy.
2. Many Argus World Quests will reward Primal Sargerite.
3. Gathering profession will have a chance to get it when Gathering the resource.
4. At Revered with Army of the Light faction, you can purchase Boon of the Lightbearer. This is has a chance of dropping when you have Boon of the Lightbearer on your gear.