What is the chemical composition of Cinnabar?

Cinnabar is a naturally occurring mineral with the chemical formula HgS (mercury(II) sulfide). It serves as the chief ore of mercury, from which the metal is extracted through the process of roasting. The mineral is easily recognizable due to its bright red color, high density, and metallic luster.

In cinnabar, mercury exists in the +2 oxidation state, and sulfur in the −2 oxidation state, forming a stable compound through covalent bonding. When heated in the presence of oxygen, cinnabar decomposes according to the following reaction:

HgS+O2→Hg+SO2HgS + O_2 → Hg + SO_2HgS+O2→Hg+SO2

During this process, mercury vapor is released and then condensed to obtain liquid mercury, while sulfur dioxide (SO₂) gas is liberated. This roasting reaction is the main industrial method for producing mercury.

Cinnabar crystallizes in the trigonal crystal system and often forms granular or massive aggregates. Its bright red pigment, known as vermilion, has been used historically in paints, art, and decoration. However, cinnabar and its pigment are highly toxic due to mercury content, and prolonged exposure can lead to mercury poisoning, affecting the nervous system and internal organs.

For comparison, other sulfide minerals have different compositions and uses:

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  ZnS (zinc sulfide) — Sphalerite, the main ore of zinc.

  
  


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  PbS (lead sulfide) — Galena, the chief ore of lead.

  
  


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  FeS (iron sulfide) — Troilite or pyrrhotite, an iron mineral.

  
  

Therefore, among the given options, the chemical composition of cinnabar is correctly identified as HgS (mercury(II) sulfide). This mineral remains the most important natural source of mercury, playing a significant role in both industrial and historical contexts.