This is a fragment is possibly the right corner of a royal nemes headdress of a nearly life-sized statue. It is dark gray or black greywacke.
From Nubia (Sudan), Kerma, K II (A) no.12. 1914: Excavated by the Harvard University–Boston Museum of Fine Arts Expedition; assigned to the MFA by the government of Sudan.
Harvard University—Boston Museum of Fine Arts Expedition