Ruby to access valley of titans disappeared from my inventory

Beat the titan boss, went back to the caravan, sold a bunch of unwanted gear (NOT the ruby) talked to zakrus (spelling?) and she commented on the ruby. Went back to valley of the titans, and the ruby was no longer in my inventory. Can't progress the game.

Also, after it disappeared, I went back and tried the boss again, just to see if it would drop (since I don't have it in my inventory) and nope, it did not drop again.

Please help.

Talking to Zarka with the Ruby would have removed it form your inventory since the quest is to give it to her. So you've done that quest now.