Question

Why the colour of the crystal disappears

Answer 1

when crystals lose or change color, it is likely the result of an energy source being applied to it.  Was your Amethyst wand left in a sunny window or outside? The sun can fade certain crystals, such as Amethyst, Rose Quartz, Celestite, Smoky Quartz, and others.  But it also could be that you and your Amethyst wand were channeling higher energies during use, that flowed through it and altered the color.  Crystals from the Quartz family definitely conduct and amplify other energies, such as Reiki and other higher dimensional frequencies.  If you were meditating with it or connecting consciously, you could have brought through higher spiritual energy that altered the Amethyst.  Since the color is fading only on one end, instead of uniformly throughout, I am drawn to believe that this is a more likely explanation

Answer 2

Explanation:

due to water of crystallisation