Real or Fake?

Hi all, I recently picked up this uncertified opal necklace of facebook marketplace for $100 in Canada, seemed to likely have been passed down judging from the interaction. Me and my sister have been arguing over whether it’s real or fake, I had bought it as a valentine’s day present for my girlfriend so I was just hoping for some more insight. Whether it’s real or fake, I bought it because it’s beautiful :)