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Mercury sulfide, mercuric 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. .
HgS is dimorphic with two crystal forms:
- red cinnabar (α-HgS), is the form in which mercury is most commonly found in nature.
- black, metacinnabar (β-HgS), is less common in nature and adopts the wurtzite crystal structure.
Crystals of red, α-HgS, are optically active. This is caused by the helices of Hg-S in the structure.
α-HgS is a direct semiconductor with an energy gap of 2.1eV at 300 K .
Preparation and Chemistry
β-HgS is precipitated as a black powder when H2S
is bubbled through solutions of Hg(II) salts. β-HgS is unreactive to all but concentrated acids.
Mercury metal is produced from the cinnabar
ore by roasting in air and condensing the vapour.
α-HgS is used as a red pigment when it is known as vermilion
. Vermilion is known to darken and this has been ascribed to conversion from red α-HgS to black β-HgS. Investigations at Pompeii where red walls when originally excavated have darkened has been ascribed to the formation of Hg-Cl compounds (e.g., corderoite
, and terlinguaite
) and calcium sulfate
, gypsum, rather than β-HgS, which was not detected.
In alchemy, known as "the Sulfur of Perfection," representing the marriage of sulfur (soul) and mercury (spirit) and the "spiritual goal of alchemical work."