Atomic Positional Parameters

Hg1 4a 0.0000 0.0000 0.0000
S1  4c 0.2500 0.2500 0.2500

Reference
D Rodic, V Spasojevic, A Bajorek and P Onnerud (1996) Journal of Magnetism and Magnetic Materials, 152, 159.

Mineral Chemistry
Metacinnabar is stable above about 600 K in the pure HgS system. However, relatively small amounts of ZnS in solid solution dramatically lower the temperature above which this mercury sulphide is stable. Compare the structure of metacinnabar with that of sphalerite, cubic ZnS.

Reaction of mercuric ions with sulphide ions in solution at ambient temperatures forms metacinnabar, not cinnabar which is the thermodynamically stable form at low temperatures.

The CHIME figure shows sphalerite structured metacinnabar. Sulphurs are yellow, and mercurys are vermillion. The unit cell is outlined.