Tiger's Eye (blue)

Hawk's eye, also called falcon's eye or blue tiger's eye, is the natural dark blue to grey-blue form of tiger's eye, a chatoyant variety of quartz. In it the enclosed crocidolite (riebeckite amphibole) fibres have not been altered to limonite and keep their original blue colour; Mindat attributes the blue to ferrous iron (Fe²⁺), compared with ferric iron (Fe³⁺) in oxidised yellow-brown tiger's eye. This natural blue is not a treatment, although dyed blue tiger's eye is also sold.