In MERP 8006 Treasures of Middle-earth, a compendium of Middle-earth magic items for MERP (a tabletop rpg), Adarcer is a material defined as:
This is a white alloy, a fusion of ang (iron), glôin ("True-coal"), and durang ("Dark-iron" or titanium). It's extremely strong, but somewhat rigid and difficult to work once forged. It can cleave iron without dulling.
In the Lord of the Rings ”fanon” fandom website, however, it's named Ardacer, with almost the same description:
Ardacer ('white alloy) was a white, metallic grey alloy of ang (iron), gloin ('true-coal' or carbon), durang ('dark-iron' or titanium) and probably magic, given that carbon steel cannot normally be alloyed with titanium. It had a high shine when polished, and was extremely strong, but somewhat rigid and difficult to work once forged. If worked properly, it could cleave iron without dulling. It was originally invented by the Dwarves. Commonly known as Dwarven steel, it was considered superior to elven steel.
I'm pretty sure the fandom entry is a typo, and the correct one is Adarcer, but I don't know.
Does anybody know the original source from Tolkien's work, so this can be clarified? Is it even something that Tolkien mentioned or it was invented by MERP writers?