[4] HgS is dimorphic with two crystal forms: β-HgS precipitates as a black solid when Hg(II) salts are treated with H2S.

[4] Mercury is produced from the cinnabar ore by roasting in air and condensing the vapour.

The tendency of cinnabar to darken has been ascribed to conversion from red α-HgS to black β-HgS.

However β-HgS was not detected at excavations in Pompeii, where originally red walls darkened, and was attributed to the formation of Hg-Cl compounds (e.g., corderoite, calomel, and terlinguaite) and calcium sulfate, gypsum.

[8] Neutralization with sulfur has been suggested to clean mercury spills, but the reaction does not proceed rapidly and completely enough for emergencies.