'Hardness' in the Bible

Who [is] like the sage? Who knows [the] interpretation of a thing? A man's wisdom makes his face shine, and the hardness of his face is changed.

{And just as} you saw the feet and the toes, {partly potter's clay} and {partly iron}, it will be a divided kingdom; and {some hardness} of the iron will be [in it], {just as} you have seen the iron mixed with the wet clay.