This is a right elbow and bent forearm fragment, much weathered but finely sculpted. The stone is black granodiorite, the break areas look almost melted (often with large pink feldspar veins or inclusions). GD4.
From Nubia (Sudan), Kerma, K III 2(2). 1913: 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