adamant

1. An unspecified mineral or rock of virtually impenetrable hardness.
2. In later use: diamond.
3. A substance that neutralizes lodestones.
4. Chiefly in of adamant: an embodiment of impenetrable hardness; the quality of not being easily destroyed or overcome; impenetrableness, imperviousness, impregnableness; also, of a person: the quality of not being easily affected emotionally; impassiveness, unmovableness. (figuratively)

الجمع adamants