Mercury(I) sulfide or mercurous sulfide is a hypothetical chemical compound of mercury and sulfur, with elemental formula Hg
2S. Its existence has been disputed; it may be stable below 0 °C or in suitable environments, but is unstable at room temperature, decomposing into metallic mercury and mercury(II) sulfide (mercuric sulfide, cinnabar).[1][2]
sestini
was invoked but never defined (see the help page).