This is a hematite conglomerate palette.
From Nuri, Pyramid IV FD, SE corner. 1918: Excavated by the Harvard University-Museum of Fine Arts Expedition; assigned to the MFA in the division of finds by the government of Sudan.
Harvard University—Boston Museum of Fine Arts Expedition
Nubian, Napatan Period, reign of Siaspiqa (?), 487–468 B.C.