I'm a 35 sneaky destruction mage. I'm in what I assume is a pretty early College quest, "Revealing the Unseen." It involves fighting your way through Mzuleft, a dwarven/falmer ruin, and manipulating some kind of dwarven artifact. I can't complete the quest. Near the end of the quest, from what I've gathered from internet searches, you have to loot a "Focusing Crystal" from a leveled mob and present it to an imperial guy in the area. The problem is, I've killed everything in the ruins, and I can't find the focusing crystal. As soon as I meet the Imperial guy to get the "find the focusing crystal" stage of the quest, the quest stops having a compass beacon. I've read that you need to kill a leveled mob (generally a Falmer Gloomlurker I guess, that's what I killed) to get the crystal. There is no crystal anywhere. I've even used console commands to spawn the crystal in my inventory and the imperial just says "until you have the crystal we have nothing to discuss" ad nauseam. I've literally restarted the game from before I even had the whole quest line (at Level 29, took a 6-level hit---i.e. turning the books in for the orc in the library) and I restarted the whole quest and I have the same problem. No focusing crystal! I've only just became a non-novice in the college! It screws up the whole game experience for me if I can't complete the magey quest line. When is this going to be fixed? Plz tell me I don't have to start over and hope for the best.

I did that quest several times without that problem, with different chars.
Do you use any Mods that may conflict with that quest?

No mods at all, unless the hi-res textures from Beth count.