what gives the gem amethyst its purplish color

Amethyst is a crystalline quartz, its colours range from light to dark purple. The purplish colour of amethyst is due to high energy radiations, such as gamma rays, from radioactive sources, the presence of trace elements and the presence of iron found in its crystal lattice. The colour cetre created by Fe4+ is a principal contributor to the colouring of amethyst.