Combine 10 of these to create a Primordium Crystal.
Once you have a stack of at least 10 of these, double click the stack (or right click it and select USE), and it will combine them.
There are two ways to obtain Shards of Primordium:
1) World Drop: every single time you win a combat, there is a random world drop chance that everyone in your party will receive 1 Shard of Primordium. This change is increased if the combat had higher rank mobs (lieutenants, elites, champions, or bosses) and also by the difficulty of the encounter.
2) Boss Loot Chests: There is a chance for most bosses to have Shards of Primordium in their loot chest, to be distributed normally as post-combat loot.