Realgar ( ), also known as arsenic blende, ruby sulphur or ruby of arsenic, is an arsenic sulfide mineral with the chemical formula α-. It is a soft, sectile mineral occurring in monoclinic crystals, or in granular, compact, or powdery form, often in association with the related mineral, orpiment (). It is orange-red in color, melts at 320 °C, and burns with a bluish flame releasing fumes of arsenic and sulfur. Realgar is soft with a Mohs hardness of 1.5 to 2 and has a specific gravity of 3.5. Its streak is orange colored. It is trimorphous with pararealgar and bonazziite.[
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Etymology
Its name comes from the Arabic rahj al-ġār (رهج الغار , "powder of the mine"), via Medieval Latin, and its earliest record in English is in the 1390s.
Uses
Realgar is a minor ore of arsenic extracted in China, Peru, and the Philippines.
Historical uses
Realgar was used by firework manufacturers to create the color white in fireworks prior to the availability of powdered metals such as aluminium, magnesium and titanium. It is still used in combination with potassium chlorate to make a contact explosive known as "red explosive" for some types of torpedoes and other novelty exploding fireworks branded as 'cracker balls', as well in the cores of some types of crackling stars.
Realgar is toxic. It was sometimes used to kill , , and ,
Realgar was commonly used in leather manufacturing to remove hair from animal pelts. Because it is a known carcinogen and an arsenic poison, and because substitutes are available, it is rarely used today for this purpose.
The ancient Greeks, who called realgar σανδαράκη (), understood that it was poisonous. From this, realgar has also historically been known in English as sandarac.
Realgar was also used by Ancient Greek apothecaries to make a medicine known as "bull's blood".[ Bull's blood is the poison that is said to have been used by Themistocles and Midas for suicide.][
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The Chinese name for realgar is 雄黃]] (Standard Chinese ), literally 'masculine yellow', as opposed to orpiment which is 'feminine yellow'.[ — On the toxicity of these medications ]
Realgar was, along with orpiment, traded in the Roman Empire and was used as a red paint pigment. Early occurrences of realgar as a red paint pigment are known for works of art from China, India, Central Asia, and Egypt. It was used in Venetian fine-art painting during the Renaissance era, though rarely elsewhere in Europe, a use which died out by the 18th century.
Occurrence
Realgar most commonly occurs as a low-temperature hydrothermal vein mineral associated with other arsenic and antimony minerals. It also occurs as volcanic sublimations and in hot spring deposits. It occurs in association with orpiment, arsenolite, calcite and barite.[
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It is found with lead, silver and gold ores in Hungary, Bohemia and Saxony. In the US it occurs notably in Mercur, Utah; Manhattan, Nevada; and in the geyser deposits of Yellowstone National Park.[
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After a long period of exposure to light, realgar changes form to a yellow powder known as pararealgar (β-). It was once thought that this powder was the yellow sulfide orpiment, but is a distinct chemical compound.
Gallery
Image:Realgar-unit-cell-3D-balls.png|The unit cell of realgar, showing clearly the molecules it contains
File:Realgar-md56a.jpg|Cluster of realgar crystals from Getchell Mine, Adam Peak, Potosi District, Humboldt County, Nevada, United States
File:Realgar-Picropharmacolite-117490.jpg|Cherry-red realgar crystals atop a matrix, and a sharp acicular spray of the rare species picropharmacolite (white needles) below
File:Réalgar, quartz, chalcopyrite, galène 90.3.9834.jpg|Crystals of realgar, quartz, chalcopyrite and galena, from Quiruvilca Mine, La Libertad, Peru
See also
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Classification of minerals
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List of inorganic pigments
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List of minerals
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Realgar wine or Xionghuang wine is a Chinese alcoholic drink that is made from Chinese liquor dosed with powdered realgar.
Further reading
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The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals. 11th Edition. Ed. Susan Budavari. Merck & Co., Inc., N.J., U.S.A. 1989.
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William Mesny. Mesny’s Chinese Miscellany. A Text Book of Notes on China and the Chinese. Shanghai. Vol. III, (1899), p. 251; Vol. IV, (1905), pp. 425–426.
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American Mineralogist Vol 80, pp 400–403, 1995 [1]
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American Mineralogist Vol 20, pp 1266–1274, 1992 [2]
External links
