The Power StonePerhaps the most famous purple/violet colored stone on Earth is this classic variant

The Power StonePerhaps the most famous purple/violet colored stone on Earth is this classic variant of the humble mineral quartz; amethyst. Amethyst’s color is the second in our list of minerals to be produced by a “Color center” – electrons that were formerly bound within the structure of the mineral are knocked loose by exposure to naturally-occurring radiation, commonly from the element potassium.For amethyst, the color starts with substitution of a little bit of iron into the structure of quartz. Quartz’s natural chemical formula is SiO2, but it is possible to include tiny bits of other elements, such as iron, substituted onto the site normally occupied by the Si. That iron can sometimes provide a weak color on its own, but if the iron is hit by radiation, that iron can lose an electron, becoming more strongly positively charged in the process. The loose electron is then trapped in the structure of quartz, creating a color center that can absorb visible light. Because the electrons in color centers are not bound to atoms, they are loose in the mineral structure and can actually be returned to their original place, hooked to the iron atoms. Sometimes, heating an amethyst can produce a different gemstone – citrine – with the reddish color from the iron. Other times, heating the amethyst can just make the color go away completely. Interestingly, exposure to too much sunlight can also weaken the color of amethyst, as the energy in sunlight is enough to move some of the electrons back to their original positions. Every so often I see a beautiful amethyst geode in a window somewhere, where it’s exposed to sunlight, and I cringe a little bit on behalf of those poor color centers.-JBBImage credit: https://flic.kr/p/47vWwRReference:http://www.geologyin.com/2015/08/changes-in-color-of-amethyst-by-heat.htmlhttps://www.researchgate.net/publication/281395725_Colored_varieties_of_the_silica_minerals -- source link

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