Cinnabar

For the moth, see Cinnabar moth.

Cinnabar
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General
Category	Mineral
Chemical formula	mercury(II) sulfide, HgS
Identification
Colour	Brownish-red
Crystal habit	Rhombohedral to tabular. Granular to massive
Crystal system	Hexagonal
Cleavage	Prismatic, perfect
Fracture	Uneven to subconchoidal
Mohs Scale hardness	2-2.5
Luster	Adamantine to dull
Refractive index	Transparent to opaque
Pleochroism	N/A
Streak	Scarlet
Specific gravity	8 - 8.2 g/cm³
Fusibility	?
Solubility	3.10^-26 g per 100 mL water
Major varieties
None

Cinnabar, sometimes written cinnabarite, is a name applied to red mercury(II) sulfide (HgS), or native vermilion, the common ore of mercury. The name comes from the Greek - "kinnabari" - used by Theophrastus, and was probably applied to several distinct substances. Other sources say the word comes from the Persian zinjifrah, originally meaning "lost"^{[[Citing sources citation needed]]}.

Contents

1 Structure
2 Properties
3 Occurrence
4 Extraction of mercury from ore
5 Other forms of cinnabar
6 References
7 External links
8 See also

Structure

HgS adopts two structures, i.e. it is dimorphous.Wells, A.F. (1984). Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6. The more stable form is cinnabar, which has a structure akin to that for HgO: each Hg center has two short Hg-S bonds (2.36 Å), and four longer Hg---S contacts (3.10, 3.10, 3.30, 3.30 Å). The black form of HgS has the zinc blende structure.

Properties

Cinnabar is generally found in a massive, granular or earthy form and is bright scarlet to brick-red in color. It occasionally occurs, however, in crystals with a metallic adamantine luster. The crystals belong to the rhombohedral (trigonal) system, and are generally of rhombohedral habit, sometimes twinned. The twinning in cinnabar is distinctive and forms a penetration twin that is ridged with six ridges surrounding the point of a pyramid. It could be thought of as two scalahedral crystals grown together with one crystal going the opposite way of the other crystal. The hardness of cinnabar is 2 - 2.5, and its specific gravity 8.998.

Cinnabar resembles quartz in its symmetry and certain of its optical characteristics. Like quartz, it exhibits birefringence. It has the highest refractive power of any mineral. Its mean index for sodium light is 3.02, whereas the index for diamond—a substance of remarkable refraction— is 2.42 and that for GaAs is 3.93. See List of indices of refraction.

Occurrence

Cinnabar was mined by the Roman Empire for its mercury content, and it has been the main ore of mercury throughout the centuries. Some mines used by the Romans remain active today. Generally cinnabar occurs as a vein-filling mineral associated with recent volcanic activity and alkaline hot springs.

Cinnabar is found in all localities that yield mercury, notably Almaden (Spain), New Almaden (California), Idrija (Slovenia), New Idria (California), Landsberg, near Ober-Moschel in the Palatinate, Ripa, at the foot of the Apuan Alps (Tuscany), the mountain Avala (Serbia), Huancavelica (Peru), Terlingua (Texas), and the province of Guizhou in China, where fine crystals have been obtained. Cinnabar is still being deposited at the present day from the hot waters of Sulphur Bank, in California, and Steamboat Springs, Nevada.

Extraction of mercury from ore

To produce liquid (quicksilver) mercury, crushed cinnabar ore is roasted in rotary furnaces. Pure mercury separates from sulfur in this process and easily evaporates. A condensing column is used to collect the liquid mercury, which is most often shipped in iron flasks. Abandoned mercury mine processing sites often contain very hazardous waste piles of roasted cinnabar calcines.

Other forms of cinnabar

Hepatic cinnabar is an impure variety from Idrija in Carniola, in which the cinnabar is mixed with bituminous and earthy matter.
Metacinnabarite is a black-colored form of HgS, which crystallizes in the cubic form.
Synthetic cinnabar is produced by treatment of Hg(II) salts with hydrogen sulfide to precipitate black, synthetic metacinnabarite, which is then heated in water. This conversion is promoted by the presence of sodium sulfide.Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.

References

External links

[MSDS for cinnabar]

For a full list of external links to MSDSs, spectroscopic data, commercial chemicals suppliers etc. for this compound, see [Chemical sources].