Vorpal shards

If you happen to fall over a Vorpal Shard, well, then you're in luck, as these give a substantial upgrade to the performance of your weapon. These can be found in Advanced or higher raid caches!
The way they work is by adding a flat +5% to Damage, Recoil, Spread, and Reload speed.
A single weapon can be starred 5 times, the first star costs 1 Vorpal Shard, while the next costs 2 etc.
Once a Weapon has hit 3 stars, it can only be upgraded further with Xen Crystals, the same above applies!
 

Xen Crystals

These Strange Crystals are the result of combing the rare material Resin and  Vorpal Shards.
Forming a dark green Crystal that glows with an otherworldly power know as  Xen Crystals.
They work the same as Shards by adding a flat +5% to Damage, Recoil, Spread, and Reload speed.
With Xen Crystals being the last items needed to obtain a  5 Starred Item.