Figure 10.

The CrSi${}_2$ structure of quartz (SiO${}_2$) and transition metal $C40$ compounds. The enantiomorphous pair of structures in the chiral space groups $P{6}_{2}22$ (180) and $P{6}_{4}22$ (181) are shown. Transition metal atoms (Cr) are green (dark), and the main group elements (Si) are shown in grey (light). (For quartz, green atoms correspond to Si and grey ones to O).