What brand is Carrie Bradshaw’s necklace?

Jessica asked: Carrie wore a beautiful necklace in episode 18 of season 6 (episode called “Splat”) that I absolutely love…She wears it at the dinner party that Aleksandr Petrovsky holds for her friends at the beginning of the episode…it was several concentric circles in diamonds…Can anyone tell me what brand it is or where I [...]