Citrine Genuine Gems suppiler Ring- Sterling Silver Yallow Citrine Ring – Citrine Ring, Sterling Silver, Yallow, art & collectibles, Gemstone ring, gift, antique, greatest selling shops, Ring art & collectibles, Citrine Genuine Gems, Ring gift for friendship day **** Rare though it is, yellow does in fact occur in quartz in Nature, if seldom, when there are traces of iron in the silicon dioxide. Historically, it has been found in Spain, on the Scottish island of Arran, in France, Hungary and in several mines overseas. Perhaps the citrine wouldn’t have been talked about any more at all if, in the middle of the 18th century, it had not been for the discovery that amethysts and smoky quartzes can also be rendered yellow by so-called burning. This heat treatment at temperatures of between 470 and 560 degrees has to be carried out very carefully and requires a great deal of experience. However, in the course of 200 years, its application has become so much a matter of course that most of the stones available in the trade today are in fact burnt amethysts or smoky quartzes. Only a trained specialist can recognise the signs of heat treatment at all, burnt stones having subtle stripes whilst the yellow of natural ones is cloudy.