An obstinate or stubborn person; pigheadedness (idiomatic).
うちの父は石頭で、なかなか意見を変えない。
My father is stubborn and hardly ever changes his mind.
あまり石頭だと周りと衝突しがちだ。
If you're too pigheaded, you tend to clash with others.
彼は石頭で、新しい方法には懐疑的だ。
He's obstinate and skeptical of new methods.
A literally hard head (like a rock); used figuratively to mean someone has a very stubborn or unyielding head.
その彫刻はまるで石頭のような表情をしている。
That sculpture has an expression like a stone head.
彼は本当に石頭で、人の忠告を聞かない。
He's really stubborn and doesn't listen to advice.