Cam Rockin' Huge Stones

Cameron Diaz was spotted at JET Nightclub at the Mirage Hotel in Las Vegas over the weekend ... wearing massive rocks on the ring finger of her left hand. Don't people in Vegas usually try to hide things that would suggest they're in a relationship?

While TMZ cameras got pretty close, our resident gemologist can't tell if these stones are real or paste.

Still, nice gems on Cam.