Polymorphing while wearing crystal plate mail, leather armor, or iron mail can cause you to merge with the armor and turn into that respective material of golem (glass, leather, or iron), with the armor returning unbroken when you revert back to your normal form.

Add a new sort of body armor that makes a compromise between studded leather and crystal plate mail - less AC than crystal plate mail, but more than studded leather (so around 5 AC), weighs more than studded leather but less than crystal plate mail (so around 300-350 aum), and doesn’t hinder spellcasting at all. Possibly, “crystal scale mail”.

Possibly crystal plate mail’s base AC will have to be boosted, or its weight lowered, in order to avoid this new armor being just better (as it stands, a gain of about 2 AC in exchange for about 100 extra weight is something most players won’t take).

Crystal plate mail is so transparent to magic that it provides no magic cancellation and can’t be enchanted, disenchanted, canceled, destroyed with destroy armor, or cursed with curse items. Possibly extend this to any armor made out of crystal (GEMSTONE). Also possibly it always generates as +0, because anything otherwise would imply that it had been enchanted previously.

Crystal gear (wands, plate mail) occasionally comes in a certain gem type.