This is a fragment from a statue with two worked surfaces. One surface is rounded. The corner where they meet is curved. The stone is grayish-green greywacke.
From Nubia (Sudan), Kerma, K III 2(1)b. 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