PPT Slide
Amethyst is translucent to transparent purple quartz. The purple color is thought to be the result of two factors: 1) small amounts of iron impurities at specific sites in the crystal structure and, 2) exposure to natural radiation in a manner similar to smoky quartz. Again, the process by which this occurs is not fully understood but it is known that exposing amethyst to sunlight for a long period of time will cause the purple color to fade. Therefore, it can be concluded that it isn't the presence of iron alone that causes the purple color or else the mineral would not fade simply due to sun exposure.