You can use amethyst for it
Yeah the most crystal I use is amethyst and ruby. Amethyst because I normally craft crystal legends that doesn't have a exclusive affix. Ruby because it has a lot of choices.
Example I want Crystal MP regen on my build.
And I already have a Druidic amulet with Crystal mp regen as a drop.
I craft that and add the other affix.
Good luck in finding the affix needed