Yes, the answer is Porcelain! I'll give Gori the point, but otaman should certainly get a cookie.
The clues:
#1: It's a gratuitous Indiana Jones reference! In "Indiana Jones and the Last Crusade", Indy's dad breaks a vase over Indy's head for a reason I won't give on the outside chance you haven't seen the movie (and if you haven't, you should.) Upon realizing that it was a replica, Dr. Henry Jones, Sr., says something like "Oh, what a relief! It was a fake!" (As a warning, I probably messed the quote up.)
#2: Porcelain is one of two unique luxuries (50%) available only from Mercantile city states (one of five types, so 20%)
#3: Porcelain is commonly referred to as China. Wu Zetian is China's leader in Civ V. That makes perfect sense, right?