Amethyst belongs to the Quartz family and is the family member that is colored purple.  It has a long history in human affairs and has been associated with royalty because it was worn with the royal purple robes of rank and priesthood.  Because it is quartz, the most common material on earth, it is part of the dust in the air that can scratch softer materials.  Therefore, quartz (hardness of 7 on the Mohs hardness scale) is considered the benchmark of a gem's hardness.  Gems that have a hardness of under 7 are considered "soft" and require special care since they can be scratched by dust, which has a hardness of 7.  

Amethyst is found in several places worldwide but is also manufactured synthetically.  It is important to deal with a reputable person when buying amethyst who will verify that it is natural and not synthetic.  Synthetic amethyst came about because of the military's need to have a pure quartz for radio transmission during World War II.  The colors were added later and sold to the public.

Currently, synthetic amethyst is pervasive in the industry and many jewelers are unaware that they are selling synthetic material.  Natural amethyst of deep, rich purple color and in sizes of 5 carats or more is usually $90 to $140/ct retail.