From WoWWiki

Bonuses for Intellect can only be obtained through Yellow gems, Orange gems and Green gems, as well as a single Meta gem.

Color	Name	Effect(s)
Yellow	[Brilliant Amber]	+4 Intellect
	[Brilliant Golden Draenite]	+6 Intellect
	[Brilliant Dawnstone]	+8 Intellect
	[Brilliant Lionseye]	+10 Intellect
Orange	[Luminous Flame Spessarite]	+3 Intellect	+7 Healing
	[Luminous Noble Topaz]	+4 Intellect	+9 Healing
	[Luminous Fire Opal]	+4 Intellect	+11 Healing
	[Luminous Pyrestone]	+5 Intellect	+11 Healing
	[Unstable Topaz]	+4 Intellect	+5 Spell Damage
	[Infused Fire Opal]	+4 Intellect	+6 Spell Damage
Green	[Dazzling Deep Peridot]	+3 Intellect	1 Mana every 5 sec
	[Dazzling Talasite]	+4 Intellect	2 Mana every 5 sec
	[Dazzling Chrysoprase]	+5 Intellect	2 Mana every 5 sec
	[Dazzling Seaspray Emerald]	+5 Intellect	2 Mana every 5 sec
	[Seer's Chrysoprase]	+4 Intellect	+5 Spirit
Meta	[Insightful Earthstorm Diamond]	+12 Intellect	Chance to restore mana on spellcast