Mercury sulfide Names IUPAC name Other names Identifiers ChemSpider ECHA InfoCard 100.014.270 EC Number UNII UN number 2025 Properties HgS Molar mass 232.65 g·mol−1 Density Melting point [1] insoluble Solubility in ethanol soluble (β-HgS)[1] Band gap 2.1 eV (direct, α-HgS)[2][page needed] −55.4×10−6 cm3/mol (α-HgS)[1] 2.9003 (α-HgS)[3] Thermochemistry[1] 48.4 J⋅mol−1·K-1 82.4 J⋅mol−1·K-1 −58.2 kJ⋅mol−1 −50.5 kJ⋅mol−1 Hazards GHS labelling: Danger H300, H310, H317, H330, H373, H410 P261, P272, P280, P302+P352, P321, P333+P313, P363, P501 NFPA 704 (fire diamond) Safety data sheet (SDS) Fisher Scientific Related compounds
Mercury sulfide or mercury(II) sulfide is a chemical compound composed of the chemical elements mercury and sulfur. It is represented by the chemical formula HgS. It is virtually insoluble in water.[4]
HgS is dimorphic with two crystal forms:
- Red cinnabar (α-HgS) is the form in which mercury is most commonly found in nature. Cinnabar has a rhombohedral crystal system. Crystals of α-HgS are optically active. This is caused by helices in the structure.[5]
- Black metacinnabar (β-HgS) is less common in nature and adopts the zinc blende crystal structure (T2d-F43m).[citation needed]
β-HgS precipitates as a black solid when Hg(II) salts are treated with H2S. The reaction is conveniently conducted with an acetic acid solution of mercury(II) acetate. With gentle heating of the slurry, the black polymorph converts to the red form.[6] β-HgS is unreactive to all but concentrated acids.[4]
Mercury is produced from the cinnabar ore by roasting in air and condensing the vapour.[4]
HgS → Hg + S
When α-HgS is used as a red pigment, it is known as cinnabar. 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.[7]
As the mercury cell as used in the chlor-alkali industry (Castner-Kellner process) is being phased out over concerns over mercury emissions, the metallic mercury from these setups is converted into mercury sulfide for underground storage.[citation needed]
It has been studied for use in photoelectrochemical cells.[8]
- Mercury poisoning
- Mercury(I) sulfide (mercurous sulfide, Hg2S), hypothetical
