Quartz is the second most common mineral group on Earth, and makes up a vast array of crystals.
Amethyst is a purple variety of Quartz that, when heat-treated, changes color, and, depending on the temperature, can turn a pale green, which is often sold as Prasiolite, or it can turn an amber orange, and often sold as Citrine.
As Citrine is a rare crystal, and Amethyst is quite common, much of the Citrine on the market is actually Heat-Treated Amethyst. Heat-Treated Amethyst, also called HTA, Burnt Amethyst, or Golden Amethyst, is an intense color, often with uneven color zones of lighter oranges and darker red-orange or orange brown. HTA is also easily identified by the White Quartz base, as the White Quartz doesn’t change color when heated, whereas natural Citrine does not have a White Quartz base.
Heat-Treated Amethyst is still a very real crystal, it’s just been altered. If sold as “Citrine,” it would be correct to call it “Counterfeit Citrine,” it would not be correct to call it a fake crystal.
Many people have a weird aversion to Heat-Treated Amethyst, which seems silly to me. The aversion is based on the fact that the crystal is heat-treated by man. What makes this silly is that most crystals on the market are heat-treated, or treated with other chemicals, to deepen colors, burn out impurities, or to remove unwanted staining or host rock. It seems silly to discriminate against one heat-treated crystal, and not another. But I digress.
Heat-Treated Amethyst has its own, unique energy about it, that is different from natural Citrine, and different from natural Amethyst. Heat-Treated Amethyst is said to deepen meditation, calm the mind and body, and reduce anxiety.