Chrysoberyl cat’s eye: Gemstone Information 

Chrysoberyl Cat’s eye is the finest of its kind; while a number of other species may show eyes when appropriately cut, their eyes are far coarser and the flat back of many chatoyant specimens enables an RI test to be made. Chrysoberyl can be tested with the spectroscope. The name ‘cat’s eye’ is used on its own for chrysoberyl only, all other chatoyant stones needing the species to be used adjectivally. Occasionally a chrysoberyl will show a four-rayed star. The finest cat’s-eyes should show a very sharp blue-white eye against a dark honey-coloured background. While chrysoberyl cat’s eye is a characteristic mineral of granite pegmatites associated with mica schists or reaction zones in ultramafic rocks, gem crystals are found most often in placers. Brazil, long a producer of the best and brightest yellow-green chrysoberyl, has in recent years become the producer of magnificent alexandrite from the Lavra de Hematita field in Minas Gerais. The best material from this deposit equals or even surpasses alexandrite from the Takovaya emerald mines, north-east of Yekaterinburg [Sverdlovsk], Russia. The colour change is pronounced in the best alexandrite from both sources. Alexandrite was named in 1982 for Tsar Alexander II. Crystals are most commonly found as star-shaped twins (trillings) reaching 2 cm across in some examples. The host rock is a mica schist. Fine yellow chrysoberyl is found in the Sanarka district of the southern Urals though the best examples come from Jacuda, Brazil. Interesting small, included alexandrites but with a marked colour change have been mined in Zimbabwe in the Smabula Forest area and from Lake Manyara, Tanzania. A colourless chrysoberyl has been found in Myanmar and a faceted example forms part of the ACD Pain collection in the Natural History Museum, London. A brown specimen from a pegmatite in the Harts Range of central Australia gave an RI of 1.765, 1.772 and 1.777 and showed an intense absorption band in the violet centred near 447 nm with another at 508 nm. Chrysoberyl has also been found at Anakie, Queensland. The finest cat’s-eyes are found in Sri Lanka though many commercial specimens are exported from Brazilian sources.