In case you've been wondering about the bonus effects of meta gems and for what damage schools they are best for, you are not alone. Frozendeath from the World of Warcraft Forums brought up a question about the Relentless Earthstorm Diamond - whether it's for melee or caster-type players.

The Relentless Earthstorm Diamond is a meta gem that sports bonuses for Agility (+12) and Critical Damage (increased by 3%). It can be made using one Earthstorm Diamond and a Simple Grinder. The question was answered by a number of other players, though Blizzard poster Drysc provided a concise answer:

It's a crit damage modifier, which means it's increasing the damage your crits do, not the chance they have to happen. It isn't specific to any school or damage type, it works for spells, melee, and ranged.

Instead of getting a 100% damage bonus with a crit, you would be getting a 103% damage bonus with a crit using that meta gem.