Nadia Petrova (Olga Fonda) wears this long spike necklace in this episode of The Vampire Diaries.

It is the With Love From CA Spike Necklace. Unfortunately it is unavailable

All Outfits from The Vampire Diaries
Other Outfits from The Vampire Diaries Season 5 Episode 11
Nadia Petrova’s Other Outfits