What does the locket Luce gets look like?

저기요 everyone, my girlfriend really loves this series. And I'd heard her talking about a locket 또는 목걸이 of some sort the main character gets. Her birthday is fast approaching, so I was hoping to buy it 또는 something which looks like it for her. But in order to do that I need to know what it looks like, so can anyone tell me?