Critical Mass

Critical Mass was a passive skill, unlocked at level 50. As of patch 2.0., Critical Mass has been removed from the game and replaced with Dominance.

In-game
Critical Mass was the most used passive ability for non-Hardcore Wizards before patch 2.0, and the second most used (after Unstable Anomaly) by Hardcore characters. It effectively allowed players to keep the cooldowns of certain spells (most notably Diamond Skin and Archon) at zero with high enough critical hit chance.

Chance of critical hit to reduce the cooldown was equal to the ability's Proc Coefficient.

Trivia

 * In the real-world nuclear physics, critical mass refers to the minimum amount of fissile material needed to sustain a nuclear chain reaction.