I saw this and thought, "Someone made a dragony ring! Neat."
FYI, that's not ametrine. Ametrine is a mix of amethyst and citrine (so, purple and yellow quartz, respectively) that can be artificially created with heat treatments of quartz (like most citrine is, to get a stronger color), and which is so far only found in nature in one part of the world: a mine in Brazil. Green and yellow like this is some other stone, most likely not any type of quartz. I'm not familiar with it, but maybe someone else can identify it-- either way, it looks amazing in this setting!