Tiger's Eye vs. Hawk's Eye: What's the Difference?

Tiger's eye and hawk's eye are both quartz pseudomorphs after crocidolite (a fibrous form of riebeckite), which is what gives them their signature chatoyancy — the silky, moving band of light across the stone.

The difference comes down to oxidation: tiger's eye has been oxidized, turning its iron content golden-brown. Hawk's eye hasn't oxidized, so it keeps a blue-grey color instead.