Studies of the materials of cylinder seals (Sax, 1986, 1991b, and in preparation a, b, c) from Western Asia throughout the 3000 years or so of their production (c. 3500 B.C. to c. 400 B.c.) have shown that there was a chronological evolution in material usage. The seals are chiefly composed of simple mineral assemblages and the selection of particular raw materials appears to have been influenced by such properties as hardness and colour. A general trend, that higher proportions of harder stones were used with advancing time, has been observed (Gorelick and Gwinnet, 1979, 1990; Sax and Middleton, 1992). The trend in increasing hardness is likely to be related to the practical advantages of sealing with harder stones and to the correspondingly greater status that they commanded; it also would have required the development of suitable lapidary techniques. This paper is concerned with trends in material usage for cylinder seals in the latter half of the third millennium B.C. during the Akkadian, Post Akkadian and Ur III periods in Mesopotamia. The evolution in material usage during these periods is markedly different from those of both earlier and later periods, perhaps indicating the operation of special factors of availability, as will be discussed. Details of the materials of the seals in the collections of the British Museum stylistically dating to the Akkadian, Post Akkadian and Ur III periods are included in the catalogue published by D. Collon (Bimson and Sax, 1982). Some minor amendments have been made to the results presented there but these do not affect the overall pattern of material usage.