Spinel, MgAl 2 O 4 (download cif), is a rare gemstone that was used to imitate rubies. The structure has face-centered cubic symmetry, and is a little heavy to understand. The general formula is AB 2 ...

The paper, published in Angewandte Chemie International Edition, reveals how t 2 occupancy—a key electronic characteristic of tetrahedral crystal ... and octahedral sites in the spinel structure ...