Slot 3 Faycite Shards

Faycite Shards are expensive augs you can place into your slot 3 aug slots in armor. Each Faycite Shard corresponds to a certain ability and does something for it. Most of the time they increase the base damage or healing of an ability or sometimes they reduce the cooldown of an ability. Since there are more Faycite shards than there are slot 3s you'll want to be picky with which ones you choose. You'll only want to grab the Faycite Shards that correspond to the abilities you most frequently use.

Faycite Shards are one of the best upgrades you can do for your character. Even though they may seem like small upgrades you must take in mind that they add to the BASE damage of your ability or spell. This makes them a whole hell of a lot more powerful than you may have assumed at first glance. This means if a faycite shard says it increases the damage done by a spell or ability by 300, all the multipliers from your AAs, focuses etc etc aren't applied to that number yet. Which means that in reality it adds much more than 300 damage.

Salus Faycite Shard: Fervid Renewal

Every expansion since the Faycite Shards have been started has a "Spell Runes" vendor. Usually this was the same vendor you traded your items too in order to get Rank II spells as well. However in TDS they have a new system in place for this and the Spell Runes vendor is just a Spell Runes vendor now. By default he will only show you the Faycite your class can use, but you can expand his list to see them all. Obviously you'll only benefit from your own classes though.

Most classes only have a few Faycite that are useful but the on the other hand there's some classes, like Necromancers, that end up needing more Faycite shards than they have slot 3s. Keep in mind too there's other things you can put into your slot 3s other than just Faycite shards. So if you have a few open slot 3s shoving in Faycite shards you won't gain much benefit from isn't really a good idea.

You can farm up the Tears of Alaris which goes into a slot 3 - or you get something like Stone of Judgment from PoWar - Icy Prism of Avoidance from LDoN and there are other slot 3s out there too.