Meta Gems and Energy

How much energy is needed to proc a meta gem and are the amounts of energy needed different from each meta gem?

Cast on crit meta gem only grants you 10 energy per crit. How much energy is need to proc this skill?

Cast on freeze grants 100 energy when you freeze and enemy, how much energy is needed to proc this skill?

Do all meta gems share energy or does each meta gem have its own energy threshold?