Citrine is a yellow form of the crystal Quartz, it does occur naturally but it is quite rare. Most of the Citrine seen on the market today is actually heat treated Amethyst. Natural Citrine is a more greeny shade of yellow, whereas heat treated Amethyst is a much darker orange, burnt colour. Some of the best natural citrine on the market today comes from Zambia, Brazil and the Congo, where it is also known as Kundalini Citrine. It has been a popular crystal for thousands of years, it was very popular with the Romans in particular, who set it into jewellery and created intaglios (carved gemstone cabochons) with it. In the 17th Century, Scottish dagger makers loved to set Citrine into the handles of daggers. Citrine made a comeback as a favourite in jewellery during the Art Deco period.