Amethyst
Amethyst gemstones ranges in colour from deep purple to pale lilac. The most popular varieties of this gem are found in Africa and South America. The name amethyst derives from the Greek word amethystos, which means "not drunk". It was used from that period through to the middle ages to help maintain clarity and sobriety when having the odd goblet or two. There are countless references to this in ancient Roman texts. Quartz will commonly contain trace amounts of iron (in the range of 10's to 100's parts per million of iron. The colour in amethyst comes from colour centres in the quartz. These are created when trace amounts of iron are irradiated (from the natural radiation in the rocks).