This is a reflectance spectrum off a polished slab. This is a reflectance spectrum off a polished slab. This is a diffuse reflectance spectrum. Amethyst color develops in iron- containing quartz after exposure to ionizing radiation.
More information is available on our ametrine page .
Smoky Quartz, Saline Valley, California. 15.5 mm thick crystal. The color of smoky quartz is due to radiation-induced color centers. One of the most prominent is centered on aluminum ions that replace silicon in the tetrahedral site.