Adamantine (ad-a-man-tine) adjective: Having the hardness of diamonds. Impervious to pleas, persuasion, requests, reason. Consisting of having the hardness of adamant. His adamantine refusal to change his mind broke his girl's heart.
My impression of adamantine is that it is a borderline word. It can be either positive of negative. It can be a fancy way of describing bull-headedness. But, I think it can also describe steadfastness of purpose. Conviction that you are on the right path, and nothing can persuade or shake you.
1. Ezekiel's adamantine forehead was a gift from God so he wouldn't fear or be dismayed by the Israelites rebelliousness, but could continue boldly proclaiming God's message.
2. The Israelites' adamantine hearts kept them from hearing God's law and messengers.
When we were in Amsterdam, we toured a diamond cutting factory. It is interesting that most diamond are first broken into 2 parts. The bigger piece is used to cut and polish the smaller piece. Only diamond is strong enough to cut diamond. Adamant itself is a very hard substance. It can refer to diamonds, other gems, steel, or hearts. While we want to be purposeful and steadfast, we don't want to have hearts hardened to other's suffering or to the Word of God.
If someone was to use adamantine to describe you, would it be positive or negative?