Was looking at leader-boards and saw that Intelligence classes uses Rubies to get armor in Chest and Pants slots. I believe dedicated Armor gem would be great addition. It could have some nice effect for weapon and helm slots as well, like:
Flawless Royal Sapphire
Weapon: Increases chance of area damage 15.0%
Helm: Increases the duration of buffs 12.5%.
Other: +780 Armor