During these interruptions, crystal growth stops momentarily, and a thin layer of different material may form or there may simply be changes in the composition or temperature of the medium that affect crystal growth.
When conditions become favorable again, amethyst crystal growth resumes, depositing more layers of material on top of the previous layer.
If these interruptions occur repeatedly during the crystal growth process, concentric layers of different shades of amethyst can form within the main crystal, creating the effect of a "ghost" or crystal within a crystal.
This phenomenon is highly valued for its rarity and aesthetic beauty, and adds a unique element to amethyst crystals.