Carved like a gargoyle visage in the side of the wall, massive, marmoreal, except that a great rumbling low breath escaped from between its lips[....]

--On, by Adam Roberts, p. 225 of the 2002 Gollancz paperback edition

MW11 says "marmoreal" means (paraphrasing) "like a marble statue."

It's possible I've seen this word before; it looks vaguely familiar. But I certainly had no idea what it meant, even from context. If I'd had to guess, I'd have guessed it meant "marmot-like." :)