This is a corner from a statue with three finished, rectilinear surfaces. The stone is a black granodiorite dense black, fine grained with many tiny mica inclusions. GD2.
From Nubia (Sudan), Kerma, K IV grave K 405 debris. 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