I rolled a witch and decided to take lightning spec. I dedicated a lot of points to +lightning dmg passives, but so far the only two lightning skill gems I have found are spark and lightning nova. I've been through the 1st difficult and did a couple quests in the next difficulty hoping to find new skills, but haven't. My two questions are: Are there any high level lightning skills (ie. Chain Lightning) and more importantly is lightning mastery even viable?

Thanks for the input.