Meta Gem (WoW)  

Meta gems are special gems that have specific requirements for use:

• Meta Gems can only be placed in a meta socket (and conversely, a meta socket can only hold a meta gem)
• Meta Gems require that you have a specific amount of other gems in order to get the bonus of the meta gem
• Meta Gems do not drop from mobs, they can only be obtained from jewelcrafters or two specific vendors. And even those vendors have unique requirements for you to purchase the gem. The do not charge gold for them, the gems are purchased with Apexis Shards or Spirit Shards.
• Also, for crafters, the uncut gems for meta gem cutting do not drop out of any mine. They must be transmuted by an alchemist.

Meta Sockets

Meta sockets are only available on certain, higher-level head slot items. Unlike other sockets that will accept a different color of gem (i.e. you can put a blue gem in a yellow socket if you want), meta sockets only accept meta gems. However like other sockets, once a gem is socketed there, there's no way to remove it and "get it back". You can replace it with another meta gem, but the existing gem in the socket is destroyed in the process.

Meta Gem Requirements

Every meta gem will have a requirement on it which must be true in order to get the benefit of the gem. In other words, if you don't meet the requirement it's nothing more than a pretty bauble, but you can't even use it for fishing. Sometimes the requirement is a hard number like "Requires at least 2 blue gems, 2 red gems and 2 yellow gems". Sometimes it's more general: "Requires more red gems than yellow gems". Note that one meta gem even has an exact number. The Imbued Unstable Diamond requires exactly 3 yellow gems. No more, no less.

Be aware that this applies to all of the gems across all of your gear, not just any additional sockets in the hem itself. It's also important to know that the non-primary color games will give you credit toward both of their colors.

Primary gem colors are: Red, Blue and Yellow Non-Primary gem colors are:

• Orange - meets Yellow and Red requirements
• Green - meets Yellow and Blue requirements
• Purple - meets Blue and Red requirements

Basically the non-primary gems will meet the requirements of both of the color sockets they fit as stated on the tooltip.

So if, in your gear, you only had 2 orange gems, you would still meet the "2 yellow, 1 red" requirements for the Swift Starfire Diamond even though that description seems to imply that you need 3 gems to meet it, the orange gem counts as both a yellow and a red gem.

Meta Gem List

World of Warcraft Wikibase™