Hawk's eye is the striking blue-grey sibling of tiger's eye. Both form when quartz grows through fibres of blue crocidolite. In tiger's eye, iron has stained the fibres golden brown, but in hawk's eye the original steely blue survives. The parallel fibres create chatoyancy, a band of light that sweeps across the stone like a cat's eye slit as you turn it. Most hawk's eye comes from the Northern Cape of South Africa, alongside its golden cousin, with more from Western Australia and India.
With quartz's hardness of 6.5 to 7 and a tough fibrous structure, hawk's eye is well suited to daily wear in rings, cufflinks and pendants. It must be cut as a cabochon with the dome aligned to the fibres, otherwise the light band disappears, so cutting quality really matters. Its moody blue makes it a favourite in men's jewellery. Care is easy: warm, soapy water and a soft brush. It is rarely imitated, though glass fibre-optic cabochons exist and look unnaturally bright.
All close relatives: tiger's eye is the iron-stained golden version, and pietersite is the same material folded into swirling patterns.
