Another old name allocated to this stone is cymophane which means ‘wave’ and ‘appearance’ because of its optical effects.Ĭhatoyancy is an interesting and unusual effect worth looking out for to add interest to either a jewellery or mineral collection. Read more: Exploring the Varieties of QuartzĪt 8.5 on the Moh’s scale of hardness, cat’s eye is a hard and durable stone and is especially popular in Japan for men’s jewellery due to its rarity.Ĭat’s eye was also a very popular stone for engagement rings in Victorian times, when it was known as chrysolite. This particular effect has led some to believe that the stone possesses supernatural qualities. As light moves across the surface the bands part and merge like the blinking eye of a cat. Images by Charlie Bexfield, Gem-A.Ĭat’s eye can also show a mesmerising ‘milk and honey’ effect where one side of the line is milky and the other translucent. The chatoyancy is caused by very fine needles which give a bright, sharply defined eye.Ī cat's eye alexandrite appearing green in daylight and purple-red under incandescent light. Some stones, such as cat’s eye alexandrite, can even exhibit colour change which is very rare, extremely expensive and desirable. Cat’s Eye GemsĬat’s eyes commonly occur in yellow, yellow-brown and greenish-yellow. It can be found in South Africa and Australia and is particularly popular for use in men’s jewellery. Image by Pat Daly, Gem-A.Ĭhatoyant quartz known as ‘tiger’s eye’ is the only chatoyant gem produced in abundance. Many species can exhibit chatoyancy including tourmaline, apatite, beryl, actinolite, demantoid garnet, scapolite, sillimanite and quartz among others but only chrysoberyl can be called simply ‘cat’s eye’, the others must be prefixed by the species name. As a result, a very definite and sharp chatoyant effect is produced. Such a stone will possess needle-like inclusions which form an effect known as ‘silk’. The type of line produced will depend on the types of inclusions the sharpest, finest line is produced in chrysoberyl, which is the only stone which may actually be called ‘cat’s eye’, without a qualifying species name. Read more: The Star of India SapphireĪs the light moves, or the observer’s eye line moves, the line appears to move too, appearing just like the way a cat’s pupil will look under a bright light.Ī chrysoberyl cabochon showing a sharp chatoyant effect. The gemstone also has to be cut as a cabochon to provide the necessary rounded surface for the line of light to be seen. In order to display this effect there must be enough fibres oriented in parallel to the base of the stone. What Causes Chatoyancy?Ĭhatoyancy occurs when a band of light is reflected from a series of thin inclusions which are parallel to each other (these may be hollow tubes or needle-like crystals of, for example, rutile or haematite). This can be seen by looking at a spool of shiny thread or some cabochon-cut gems. The term ‘chatoyancy’, deriving from the French for ‘shining like a cat’s eye’, denotes the effect that occurs when a bright light is shone onto a rounded, reflective surface and causes light to be reflected back in narrow line perpendicular to the observer’s line of sight. Gem-A's Collection Curator, Barbara Kolator FGA DGA explains chatoyancy and highlights some of the many gems in which it can occur.Ĭhatoyancy is the name given to the ‘cat’s eye’ optical phenomenon which can be seen in certain gemstones. Chatoyancy is the gemmological name given to the curious optical effect in which a band of light is reflected in certain cabochon-cut gemstones, creating an appearance similar to light bouncing off a cat's eye.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |