Cinnabar
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- For the moth, see Cinnabar moth.
| Cinnabar | |
|---|---|
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| General | |
| Category | Mineral |
| Chemical formula | mercury(II) sulfide, HgS |
| Identification | |
| Color | 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 |
| Streak | Scarlet |
| Specific gravity | 8 - 8.2 g/cm³ |
| Solubility | 3.10-26 g per 100 mL water |
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"[citation needed].
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[edit] Structure
HgS adopts two structures, i.e. it is dimorphous.[1] 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.
[edit] 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 non-metallic adamantine luster. Cinnabar has a rombohedral bravais lattice, and belongs to the hexagonal crystal system, trigonal division. Its crystals grow usually in a massive habit, though they are 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.
[edit] Occurrence
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 Almadén (Spain), New Almaden (California), Idrija (Slovenia), New Idria (California), Landsberg, near Obermoschel 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.
[edit] Mining and extraction of mercury
Cinnabar was mined by the Roman Empire both as a pigment and 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.
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.
Because of the high toxicity of mercury, both the mining of cinnabar and refining for mercury are hazardous and historic causes of mercury poisoning. In particular, the Romans used convict labor in their mines as a form of death sentence. The Spanish also used shorter term convict labor at the Almadén mines, with a 24% overall fatality rate in one 30 year period.
Abandoned mercury mine processing sites often contain very hazardous waste piles of roasted cinnabar calcines. Water runoff from such sites is a recognized source of ecological damage.
Cinnabar was often used in royal burial chambers during the peak of Mayan civilization. The red stone was inserted into limestone sarcophagi, both as a decoration and, more importantly, to deter vandals and thieves with its well-known toxicity.[citation needed]
[edit] Medicinal use
Although cinnabar is known to be highly toxic,[1] it is nevertheless used (as is arsenic), in powdered form mixed with water, in traditional Chinese medicine (TCM). Although cinnabar is not used in Western medicine, TCM practitioners sometimes prescribe it as part of a medicinal mixture, often on the basis of the concept of "using poison to cure poison." Used internally, cinnabar is believed to clear away "heat" and tranquilize the mind. It is also used as a tonic to reduce the incidence of heart palpitations, restlessness, and insomnia, and to treat sore throats and cold sores that occur in the mouth and tongue. In addition, cinnabar is applied externally to treat certain skin disorders and infections.[2]
[edit] 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.[2]
[edit] References
- ^ Wells, A.F. (1984). Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.
- ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
