Realgar

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 in white flame and star compositions and to produce yellow smoke in daytime fireworks.

Realgar has been used to kill weeds, insects, and rodents, even though more effective arsenic-based anti-pest agents are available such as cacodylic acid, , an organoarsenic compound used as an herbicide.

Realgar was also used by Ancient Greek apothecaries to make a medicine known as "bull's blood". The Greek physician Nicander described a death by "bull's blood", which matches the known effects of arsenic poisoning. Bull's blood is the poison that is said to have been used by Themistocles and Midas for suicide.

The Chinese name for realgar is 雄黃 (Mandarin zh), literally 'masculine yellow', as opposed to orpiment which is 'feminine yellow'.

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. It was also used as medicine. Other traditional uses include manufacturing lead shot, printing, and dyeing calico cloth. It was used to poison rats in medieval Spain and in 16th century England.

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.

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.

After a long period of exposure to light, realgar changes form to a yellow powder known as pararealgar (). 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

References

References

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