Real Amethyst stones will have color zoning including shades of white and blue along with purple. A real Amethyst gem won't have any bubbles but may have threads and impurities beneath the surface. Amethyst is one of the most popular gemstones.
What type of amethyst is most valuable?
Siberian Amethyst
How can you tell if amethyst is rare?
Authentic gems should be slightly imperfect. There should be some color zoning and the shade should have tones of white or blue in addition to purple. A gem that is one particular shade of purple throughout is likely a fake. You should also look for things like bubbles and cracks within the amethyst.