| Realgar | |
|---|---|
 Realgar crystals, Royal Reward Mine,King County, Washington, US | |
| General | |
| Category | Sulfide mineral |
| Formula | As4S4 or AsS |
| IMA symbol | Rlg[1] |
| Strunz classification | 2.FA.15a |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (sameH-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 andcarcinogenic.Disintegrates on long exposure to light to a powder composed ofpararealgar orarsenolite andorpiment. |
| References | [2][3][4][5][6] |
Realgar (/riˈælɡɑːr,-ɡər/ree-AL-gar, -gər), also known asarsenic blende,ruby sulphur orruby of arsenic, is anarsenic sulfide mineral with the chemical formulaα-As4S4. It is a soft, 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, and burns with a bluish flame releasing fumes of arsenic and sulfur. It istrimorphous with pararealgar and bonazziite.[2]
Its name comes from the Arabicrahj 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 in white flame and star compositions and to produce yellow smoke in daytime fireworks.[11][12]
Realgar has been used to kill weeds, insects, and rodents,[13] even though more effective arsenic-based anti-pest agents are available such ascacodylic acid,(CH3)2As(O)OH, anorganoarsenic compound used as an herbicide.[citation needed]
Realgar was also used by Ancient Greek apothecaries to make a medicine known as "bull's blood".[14] The Greek physicianNicander described a death by "bull's blood", which matches the known effects of arsenic poisoning.[14] Bull's blood is the poison that is said to have been used byThemistocles andMidas for suicide.[14]
The Chinese name for realgar is雄黃 (Mandarinxiónghuáng), literally 'masculine yellow', as opposed to orpiment which is 'feminine yellow'.[15]
Realgar was, along with orpiment, traded in theRoman 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 theRenaissance era, though rarely elsewhere in Europe, a use which died out by the 18th century.[16] It was also used as medicine. Other traditional uses include manufacturing lead shot, printing, and dyeing[how?]calico cloth. It was used to poison rats in medieval Spain and in 16th century England.[17]
Realgar most commonly occurs as a low-temperaturehydrothermalvein mineral associated with other arsenic and antimony minerals. It also occurs asvolcanic sublimations and in hot spring deposits. It occurs in association with orpiment,arsenolite,calcite andbarite.[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.[18]
Red Arsenic... They are very useful in making white stars, especially as they take fire far more easily than those made from antimony.
