Amethyst phantom means that there is a shadow like pattern other minerals in the crystal, so you will see subtle layers of different colours within the amethyst.
 
Amethyst is a purple-coloured quartz crystal. Purple shades vary from light lavender to deep violet. Amethyst crystals have a spiritual quality to them and can be used to help individuals tap into higher levels of consciousness. It can serve as a bridge between physical and ethereal frequencies, creating an opening for enlightenment.