Certain races should be able to forge using materials other races can’t:

• Dwarves can forge with crystal items, and possibly stone.
• Orcs can forge with stone items. Bone would be more flavorful for orcs, but less flavorful in being something that can actually be forged with.

Magic flutes have a roughly 1% chance of generating as gemstone (or glass).

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.