adamant

As an adamant harder than flint have I made thy forehead: fear them not, neither be dismayed at their looks, though they be a rebellious house.

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.

His mercy is manifest to every creature; and he hath separated his light from the darkness with an adamant.

But the holy and God-fearing mother wailed not with this lamentation over any one of them, neither besought she any to escape death, nor lamented over them as dying men; but, as though she had a soul of adamant and were bringing forth the number of her sons, for a second time, into immortal life, she besought rather and entreated of them that they should die for religion's sake.