How do quartz develop in different colours?

Quartz and its colored varieties. For information on other polymorphs of silica, see http://minerals.gps.caltech.edu/Silica_Polymorphs/index.html. Quartz mine in Minas Gerais, Brazil. Iron-containing varieties: Amethyst. Large geodes of amethyst occur in basalts in southern Brazil and northern Uraguay. read more

Chemical impurities get evenly spread, or preferentially distributed (depending on water and other interactions) into the pure quartz matrix. Because of the clear character of this mineral, light is refracted and impurities alter the wavelengths as they travel through the mineral, causing it to appear a variety of possible colors. read more

Interference color varies according to two parameters. The birrefringence of the section (which is a property of the mineral and the direction of the section) and the width of the section. This usually means that sections made of the same mineral on the same orientation will have different interference colors if one is thicker than the other. read more