Compact granite. The "necking" is so shallow as to be hardly a groove at all. On one side is a hollow made by abrasion. The opposite side is smoother. Edge blunt.
From Giza G 2150. 1906: excavated by the Harvard University–Museum of Fine Arts Expedition; assigned to the MFA by the government of Egypt. (Accession Date: November 8, 1906)
Harvard University—Boston Museum of Fine Arts Expedition