This stone is one of the most affordable AND most popular stones! Typically, gold in color, it also comes in orange brown and red shades of transparent quartz. Natural citrine is mostly pale yellow to golden in color.
Most citrine found in the market is heat-treated amethyst, and thus has a reddish tint. Though most citrine is heat-treated, the most sought after and valuable are indeed the natural citrine stones. This at least makes it easy to determine what citrine stones are natural and which are heat-treated. The chief determinants in value are color, clarity, and luster. Since citrines are transparent, it should be fairly easy to determine the clarity.
The largest natural deposit of citrine is in Brazil, while other sources are found in Argentina, Madagascar, Myanmar (Burma), Namibia Russia, Scotland and Spain.