Take a look at the ground around you. Chances are you’ll find some sand. Sand, quite frankly, is boring stuff. It’s rather dull looking, and it’s … pardon the pun … common as dirt.
One of the major components of sand is silica or quartz – known chemically as silicon dioxide, SiO2. Regular quartz can form pretty crystals, but these crystals are still rather dull in terms of color.
When quartz crystals form, they generally don’t do so in a chemically clean environment. In other words, there’s an awful lot of other stuff around. That other stuff can get trapped inside the quartz crystals, leading to imperfections in the quartz structure.
When these impurities are large enough to be seen with the naked eye, they’re called inclusions. Often, inclusions make crystalsl less valuable.
Sometimes impurities get into a crystal at the atomic level. These impurities (called interstitial impurities or substitutional impurities depending on where in the crystal structure they are) can’t be seen with the naked eye. But … if there are enough of them, these impurities affect the crystals properties in a way that can be easily detected.
Take that silicon dioxide – boring ol’ sand – we mentioned earlier. If silicon dioxide crystals form in such a way that the crystal contains trapped iron or manganese ions**, the crystals will look like this:
![[A sample of amethyst]](http://whenchemistsattack.com/blogfiles/amethyst_450.jpg)
A sample of amethyst
Quite a difference! This is amethyst, an impure (but much prettier) form of quartz.
![[Amethyst close-up!]](http://whenchemistsattack.com/blogfiles/amethyst_hires.jpg)
A different sample of amethyst, up close. Click to see a high resolution image of the whole stone (378K).
Just keep in mind that the impurities in the silicon dioxide crystal that transform it from boring quartz to beautiful amethyst!
**I’ve seen the purple color of amethyst described as being caused by both iron and manganese impurities