From WoWWiki

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

Color	Name	Effect(s)
Meta	[Tenacious Earthstorm Diamond]	+12 Defense	Chance to Restore Health on hit
	[Eternal Earthstorm Diamond]	+12 Defense	+10% Shield Block Value
Yellow	[Facet of Eternity]	+12 Defense
	[Thick Lionseye]	+10 Defense
	[Thick Dawnstone]	+8 Defense
	[Thick Golden Draenite]	+6 Defense
	[Thick Amber]	+4 Defense
Orange	[Champion's Fire Opal]	+4 Defense	+5 Strength
	[Glimmering Fire Opal]	+4 Defense	+5 Parry Rating
	[Glistening Fire Opal]	+5 Defense	+4 Agility
	[Stalwart Fire Opal]	+5 Defense	+4 Dodge Rating
Green	[Effulgent Chrysoprase]	+5 Defense	2 Mana every 5 sec
	[Enduring Seaspray Emerald]	+5 Defense	+7 Stamina
	[Enduring Chrysoprase]	+5 Defense	+6 Stamina
	[Enduring Talasite]	+4 Defense	+6 Stamina
	[Enduring Deep Peridot]	+3 Defense	+4 Stamina