Hawk's eye

Hawk's eye is a fibrous variety of quartz in colours from dark blue to blue-grey and bluish green. It forms in the same deposits and in the same way as tiger's eye; the only difference is that the iron in its crocidolite (blue asbestos) fibres has not oxidised. So instead of golden yellow it shows the original bluish colour of crocidolite. When cut as a dome and polished, a gliding band of light appears on its surface, recalling the eye of a bird of prey. Most of it comes from South Africa's Northern Cape.

Both are quartz with crocidolite fibres, formed in the same deposits. When part of the iron in the fibres oxidises, the stone becomes golden-yellow and brown tiger's eye; where the iron stays unoxidised, blue-grey hawk's eye forms.

Jewellery: it is usually cut as a cabochon to show the band of light best, and made into ring stones, pendants and beads. Accessories: it is also used in small decorative pieces such as brooches and tie pins. Tumbled stones: it is sold as small pebbles polished in a rotating tumbler. Inside other stones: it also appears in pietersite, a stone formed when pieces of hawk's eye and tiger's eye were broken and cemented together again.

It has a hardness of 7 on the Mohs scale. It scratches glass and steel; a steel knife cannot scratch it. Its specific gravity is 2.65–2.66 g/cm³.

Its best-known localities: Asbestos Mountains (between Prieska and Griquatown), Northern Cape, South Africa; Western Australia; Namibia.

Its colour is dark blue, blue-grey or bluish green; turned under a light, a silky, bright band glides across the surface. The same stone may contain golden or brown bands of tiger's eye; the gradual change from blue to golden zones shows that the two stones are the same material. It is as hard as quartz (6.5–7): it scratches glass, and a steel knife struggles to scratch it. Fibre-optic glass: shows a similar band of light and is made in many colours; seen from the side, its fibres form a very regular, honeycomb-like pattern.

On the “street to diamond” value ladder it sits on step 5 of nine: Ornamental stone. Hawk's eye is a plentiful ornamental stone. Its value depends mainly on a sharp, bright band of light, deep and even blue colour, regular fibres, and a stone cut as a dome with the fibres parallel to its base and well polished. Naturally coloured, untreated stones are worth more than those lightened with acid, dyed or heated. Striking pieces that show blue and golden bands together are also sought after.

Today crystal-therapy websites and stone sellers present hawk's eye as a “stone of sight and intuition” and claim that it sharpens focus and intuition. The same sources claim that the stone protects travellers and eases a fear of flying and anxiety. There is no scientific evidence that hawk's eye strengthens intuition, protects travellers or eases anxiety; its eye-like shimmer is a physical effect of parallel fibres reflecting light. Rough stone contains asbestos fibres, so it should not be cut or ground into powder at home. Problems with eyesight call for an eye doctor. This section reports beliefs; it is not health information. There is no scientific evidence for these claims and no stone replaces medical treatment.

Hawk's eye contains fibres of crocidolite, an asbestos mineral. Because the fibres are locked inside hard quartz, wearing and handling polished stones is harmless. Dust produced when cutting, grinding or sanding rough material, however, should not be inhaled: work wet and wear a suitable dust mask.