Ezekiel 3:9 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. (WEB KJV JPS ASV DBY WBS YLT RSV)
Zechariah 7:12 Yea, they made their hearts as an adamant stone, lest they should hear the law, and the words which the LORD of hosts hath sent in his spirit by the former prophets: therefore came a great wrath from the LORD of hosts. (KJV JPS ASV DBY WBS YLT RSV)