Adamant isn't a Tolkien creation. It often refers to diamonds, but
historically can mean any hard, "unbreakable" stone, metal or other
substance. It's in the dictionary
I'm having enough trouble this end just keeping up with the submissions,
never mind tracking down the etymology of all submissions. If people
could take the time to provide links and get the right description, it
would go a long way to helping.
Thanks,
Reid.