The compound commonly known as cinnabar has the chemical formula HgS, a combination of mercury and sulphide in one-to-one molar ratio. The chemical is formally known as mercuric sulphide. Compounds of mercury tend to be white powders, but mercuric sulfide is a deep red solid that turns black when exposed to sunlight (for long periods of time?). For its impressive red color, the Chinese--and I assume other civilizations--used cinnabar as a dye for cloth. Mercury can be extracted by heating mercuric sulfide past its melting point of 540 C, temperature at which the mercury will vaporize and can be collected.