'Harder' in the Bible

O Yahweh, don't your eyes look on truth? You have stricken them, but they were not grieved. You have consumed them, but they have refused to receive correction. They have made their faces harder than a rock. They have refused to return.

As an adamant harder than flint have I made your forehead: don't be afraid of them, neither be dismayed at their looks, though they are a rebellious house.