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 ...

Another perspective on spinel comes from looking at its unit shell (counter-intuitive, I know). First we show the Mg atoms, which form an fcc aray, plus 4 more atoms inside the cube. Those 4 are ...

Long considered a kind of poor man’s ruby, the gemstone has come into its own. By Kathleen Beckett Pity the poor spinel. The gemstone that many people have never heard of has been saddled for ...