Stars and Cats-Eyes

I’ve been told off for being too “sciency” and that it is “boring”. I could relate stories about some of my customers, such as a well known TV presenter who said she had “hobbit feet”and her hands were of the same unusual proportion (they weren’t), or another well known lady who insisted she wanted a “goat-eye” stone; turned out she meant cat’s eye, which segues nicely into this month’s article, and avoids me spilling any secrets.

Chatoyancy, better known as cats-eye, is when a band of light appears inside the stone when an external light hits its surface. This optical effect is caused by inclusions, usually rutiles. Rutiles are minerals that have crystallized in long needlelike formations during the creation of the stone.

These rutile hairs form in parallel clusters and the cutter will cut the stone in a cabochon (a rounded, domed top with a flat, matte underside) with the rutiles going in one direction, in line with the base of the stone. It is important that the underside of the stone does not allow light to pass through.  Examples of cats-eyes are found in alexandrite and all chrysoberyls, aquamarines, tigers-eye, moonstones and quartzes.

Asterism or a star effect has all of the above but with slightly differing structures. Four or, more probably, six-legged stars are formed in gems such as sapphires and rubies. A sapphire crystal is six-sided, and as the crystals grow, the rutiles grow aligning themselves with the six-sided crystal structure.

Again, these stones will be cabochon cut, and light hitting the stone will, if the stone has been cut accurately, produce three intersecting bands of light, thus forming a six- rayed star.  Unlike chatoyancy where the band of light can be rocked from side to side, in a star gem the legs should be straight, coming from a central point and should be at 60 degree angles. And, of course, the more perfect the star, the higher the price.

While on the subject of rutiles, this is rutile quartz ring, a quite beautiful and relatively inexpensive stone. The golden rutiles in these stone are made from titanium dioxide - and that’s the science bit!  If you have any jewellery questions or jewellery design queries, please contact me.  ps My thanks to Doris Oakley for her kind comments on this column!

StrawberryWood

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www.strawberrywood.co.uk

Strawberrywood

StrawberryWood