This amulet of polished hematite represents a headrest. Such amulets were common in Late Period burials, where their magic was intended to lift the head of the deceased at the moment of resurrection.
From Giza: G 7652A, Room IV. April 29, 1929: Excavated by the Harvard University–Museum of Fine Arts Expedition; assigned to the MFA by the government of Egypt.
Harvard University—Boston Museum of Fine Arts Expedition