The description matches almost word for word the classical desciption of the Ox Head demon. Ox Head and Horse Face are the two most recognisable of the lowest ranking demons of Hell. They do the menial work, such as it is, in punishing sinners. Those who have interacted with them have claimed them to be strong, but not overly bright. Their unnatural bodies do have some resistance to normal weapons, but a hard enough blow can and will hurt them. Both the jade and silver, as pure materials, will ignore their unnatural toughness.