the Crystal Knowledge thread

[Fastidious Emanations]

Amethyst represents the most popular variation of naturally colored quartz. Owing to its magical purple color, it was highly esteemed in the past. The physical origin of its color, however, is not completely explained up to date. Today, it is generally accepted that Amethyst ’s purple color is a results of the presence of iron ions within the quartz crystal lattice. These iron ions constitute the so-called "color centers", responsible for the change of color from white to the various shades of purple.

In fact, Amethyst can be synthesized in laboratory by adding iron atoms during the growth of quartz, followed by subsequent gamma or X-ray irradiation. Natural quartz contains certain amount of iron, but the mere presence of iron is not enough. It is necessary to have a source of high energy radiation capable of releasing one electron from the iron ion and thereby creating the color center which will be responsible for the characteristic purple Amethyst color. The released electrons from these color centers are trapped inside the crystal as a whole and in normal circumstance they do not play an important role. However, if there were enough energy at their disposal, these electrons would be able to go back to their original position, changing the purple color of Amethyst to some other shade.

This excess of energy could be provided, for example, by heating Amethyst at temperatures above 570 degrees Fahrenheit (300 degrees Celsius). In this process, Amethyst starts to loose its characteristic color, taking on the yellowish color of citrine, or in some cases, on the green color of green amethyst - prasiolite. This sort of "bleaching" of Amethyst could in principle happen also in cases of extensive light exposure, although Amethyst is relatively stable against light of moderate intensity.

~http://www.sunnyray.org/Amethyst.htm