Realgar

Realgar
Realgar crystals, Royal Reward Mine, King County, Washington, US
General
Category	Sulfide mineral
Formula (repeating unit)	As4S4 or AsS
IMA symbol	Rlg[1]
Strunz classification	2.FA.15a
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	P21/n (no. 14)
Unit cell	a = 9.325(3) Å b = 13.571(5) Å c = 6.587(3) Å β = 106.43°; Z = 16
Identification
Color	Red to yellow-orange; in polished section, pale gray, with abundant yellow to red internal reflections
Crystal habit	Prismatic striated crystals; more commonly massive, coarse to fine granular, or as incrustations
Twinning	Contact twins on {100}
Cleavage	Good on {010}; less so on {101}, {100}, {120}, and {110}
Tenacity	Sectile, slightly brittle
Mohs scale hardness	1.5–2
Luster	Resinous to greasy
Streak	Red-orange to red
Diaphaneity	Transparent
Specific gravity	3.56
Optical properties	Biaxial (−)
Refractive index	nα = 2.538 nβ = 2.684 nγ = 2.704
Birefringence	δ = 0.166
Pleochroism	Nearly colorless to pale golden yellow
2V angle	40°
Dispersion	r > v, very strong
Other characteristics	Toxic and carcinogenic. Disintegrates on long exposure to light to a powder composed of pararealgar or arsenolite and orpiment.
References	[2][3][4][5][6]

Realgar (/riˈælɡɑːr, -ɡər/ ree-AL-gar, -⁠gər), also known as ″arsenic blende″, ″ruby sulphur″ or ″ruby of arsenic″, is an arsenic sulfide mineral with the chemical formula α-As₄S₄. 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 (As₂S₃). 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.^[2]

Its name comes from the Arabic rahj al-ġār (رهج الغار [rahdʒælɣaːr] listen^ⓘ, "powder of the mine"), via Medieval Latin, and its earliest record in English is in the 1390s.^[7][8][9]

Realgar is a minor ore of arsenic extracted in China, Peru, and the Philippines. ^[10]

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.^{[citation needed]}

Realgar is toxic. It was sometimes used to kill weeds, insects, and rodents,^[11] even though more effective arsenic-based anti-pest agents are available such as cacodylic acid, (CH₃)₂As(O)OH, an organoarsenic compound used as herbicide.

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 (sandarákē), 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".^[12] The Greek physician Nicander described a death by "bull's blood", which matches the known effects of arsenic poisoning.^[12] Bull's blood is the poison that is said to have been used by Themistocles and Midas for suicide.^[12]

The Chinese name for realgar is 雄黃 (Mandarin xiónghuáng), literally 'masculine yellow', as opposed to orpiment which is 'feminine yellow'.^[13]

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 European fine-art painting during the Renaissance era, a use which died out by the 18th century.^[14] 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.^[15]

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.^[2]

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.^[5]

After a long period of exposure to light, realgar changes form to a yellow powder known as pararealgar (β-As₄S₄). It was once thought that this powder was the yellow sulfide orpiment, but is a distinct chemical compound.^[16]

• 
  The unit cell of realgar, showing clearly the As₄S₄ molecules it contains
• 
  Cluster of realgar crystals from Getchell Mine, Adam Peak, Potosi District, Humboldt County, Nevada, United States
• 
  Cherry-red realgar crystals atop a matrix, and a sharp acicular spray of the rare species picropharmacolite (white needles) below
• 
  Crystals of realgar, quartz, chalcopyrite and galena, from Quiruvilca Mine, La Libertad, Peru

• Classification of minerals
• List of inorganic pigments
• List of minerals
• Realgar wine or Xionghuang wine is a Chinese alcoholic drink that is made from Chinese liquor dosed with powdered realgar.^[17]

• The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals. 11th Edition. Ed. Susan Budavari. Merck & Co., Inc., N.J., U.S.A. 1989.
• 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.
• American Mineralogist Vol 80, pp 400–403, 1995 [1]
• American Mineralogist Vol 20, pp 1266–1274, 1992 [2]

Wikimedia Commons has media related to Realgar.

• Mindat.org: Pararealgar