Mercury sulfide
Overview
 
Mercury sulfide, mercuric sulfide, or mercury(II) sulfide is a chemical compound composed of the chemical elements mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

 and sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

. It is represented by the chemical formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

 HgS. It is virtually insoluble in water.
HgS is dimorphic with two crystal forms:
  • red cinnabar
    Cinnabar
    Cinnabar or cinnabarite , is the common ore of mercury.-Word origin:The name comes from κινναβαρι , a Greek word most likely applied by Theophrastus to several distinct substances...

     (α-HgS, hexagonal
    Hexagonal crystal system
    In crystallography, the hexagonal crystal system is one of the 7 crystal systems, the hexagonal lattice system is one of the 7 lattice systems, and the hexagonal crystal family is one of the 6 crystal families...

    , hP6, P3221), is the form in which mercury is most commonly found in nature.
  • black, metacinnabar (β-HgS), is less common in nature and adopts the zinc blende (T2d-F-43m) crystal structure
    Crystal structure
    In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry...

    .

Crystals of red, α-HgS, are optically active.
 
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