Realgar, α-As4S4, is an arsenicsulfide mineral, also known as "ruby sulphur" or "ruby of arsenic". 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 alacranite and pararealgar. Its name comes from the Arabic rahj al-ġār, via Catalan and Medieval Latin, and its earliest record in English is in the 1390s.
Uses
Realgar, orpiment, and arsenopyrite provide nearly all the world's supply of arsenic as a byproduct of smelting concentrates derived from these ores. 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 is sometimes used to kill weeds, insects, and rodents, even though more effective arsenic-based agents are available. Realgar was commonly applied in leather manufacturing to remove the hair from animal pelts. Because realgar is a known carcinogen, and an arsenic poison, and because competitive substitutes are available, it is rarely used today for this purpose.
Historical uses
The ancient Greeks, who called it sandaracha, understood that it was poisonous. It was used to poison rats in medieval Spain and in 16th-century England. 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". 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 xionghuang 雄黃, literally 'masculine yellow', as opposed to orpiment which was 'feminine yellow'. Its toxicity was also well known to them, and it was sprinkled around houses to repel snakes and insects, as well as being used in Chinese medicine. Realgar is mixed with huangjiu to make realgar wine, which is consumed during the Dragon Boat Festival in order to ward off evil, alluding to its repellent properties. Realgar was, along with orpiment, a significant item of trade in the ancient Roman Empire and was used as a red paint pigment. Early occurrences of realgar as a red painting 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. It was also used as medicine. Other traditional uses include manufacturing lead shot, printing and dyeing calico cloth.
