06-08. Spinel #5.
This one could have come from one of Escher’s sketch book. More simply, it is 4 different sizes of the same polyhedral arrangement of a spinel unit cell.
Prof. Kosters wrote an interesting article on Escher and gemology. It really brings to light how and to what degree Mathematics and Applied Sciences affected his work.
From a resource by Peterson, Lager, and Hitterman.