Realgar

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Realgar

Realgar, a

Polymorphism (materials science)

Polymorphism in materials science is the ability of a solid material to exist in more than one form or crystal structure. Polymorphism can potentially be found in any crystalline material including polymers, minerals, and metals, and is related to allotropy, which refers to chemical elements....
-As₄S₄, is an arsenic

Arsenic

Arsenic is a well-known chemical element that has the symbol As and atomic number 33. Arsenic was first documented by Albertus Magnus in 1250....
sulfide

Sulfide

The term sulfide refers to several types of chemical compounds containing sulfur in its lowest oxidation number of −2.Formally, "sulfide" is the dianion, S2−, which exists in strongly alkaline aqueous solutions formed from H2S or alkali metal salts such as Li2S, Na2S, and K2...
mineral. 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

Orpiment

Orpiment, Arsenic trisulfide, is a common monoclinic arsenic sulfide mineral. It has a Mohs hardness of 1.5 to 2 and a specific gravity of 3.46....
(As₂S₃).

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Realgar, a

Polymorphism (materials science)

Arsenic

Arsenic is a well-known chemical element that has the symbol As and atomic number 33. Arsenic was first documented by Albertus Magnus in 1250....
sulfide

Sulfide

Orpiment

Orpiment, Arsenic trisulfide, is a common monoclinic arsenic sulfide mineral. It has a Mohs hardness of 1.5 to 2 and a specific gravity of 3.46....
(As₂S₃). It is orange-red in colour, 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

Specific gravity

Specific gravity is defined as the ratio of the density of a given solid or liquid substance to the density of water at a specific temperature and pressure, typically at 4?C and , making it a dimensionless quantity ....
of 3.5. Its molecular weight is 106.99. Its streak

Streak (mineralogy)

The streak of a mineral is the color of the powder produced when it is dragged across an unweathered surface. Unlike the apparent color of a mineral, which for most minerals can vary considerably, the trail of finely ground powder generally has a more consistent characteristic color, and is thus an important diagnostic tool in mineral identi...
is orange colored. Realgar has a sub-metallic luster

Lustre (mineralogy)

Lustre is a description of the way light interacts with the surface of a crystal, rock , or mineral. For example, a diamond is said to have an adamantine lustre and pyrite is said to have a metallic lustre....
.

Its name comes from Arabic rahj al-ghar – 'powder of the mine,' via Catalan

Catalan language

Catalan is a Romance languages, the national language and official language of Andorra, and a official language in the Autonomous Communities of Spain of the Balearic Islands, Catalonia and Valencian Community and in the city of Alghero in the Italy List of islands in the Mediterranean of Sardinia....
, Middle Latin, and Middle English

Middle English

Middle English is the name given by historical linguistics to the diverse forms of the English language spoken between the Norman conquest of England of 1066 and about 1470, when the #Chancery Standard, a form of London-based English, began to become widespread, a process aided by the introduction of the printing press into England by William...
, though this comes through a misreading, the original name was rahj al-far – 'rat powder', due to its use as a rodenticide. In India, realgar is known as manseel, and orpiment as hartal.

It was, along with orpiment

Orpiment

Orpiment, Arsenic trisulfide, is a common monoclinic arsenic sulfide mineral. It has a Mohs hardness of 1.5 to 2 and a specific gravity of 3.46....
, a significant item of trade in the ancient Roman Empire

Roman Empire

The Roman Empire was the Roman Republic phase of the Ancient Rome, characterised by an autocracy form of government and large territorial holdings in Europe and around the Mediterranean....
and was used as a pigment

Pigment

A pigment is a material that changes the color of light it Reflection as the result of selective color absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which the material itself emits light....
and a medicine. It was also used as a medicine in China

China

China is a Culture of China, an ancient civilization, and, depending on perspective, a national or multinational entity extending over a large area in East Asia....
and "is made up into household ornaments, such as wine pots, wine cups, images, paperweights, and various other kinds of ornaments and charms, to be kept near at hand in use, or worn about the person, with a view of warding off disease."

It is commonly held that after a long period of exposure to light realgar changes form to a yellow powder known as pararealgar

Pararealgar

Pararealgar is an arsenic sulfide material with the chemical formula arsenicsulfur. It forms gradually from realgar under exposure to light. Its name derives from the fact that its elemental composition is identical to realgar, As4S4....
(ß-As₄S₄). It was once thought that this powder was the yellow sulfide orpiment, but has been recently shown to be a distinct chemical compound.

Realgar, orpiment, and arsenopyrite

Arsenopyrite

Arsenopyrite is an iron arsenic sulfide . It is a hard metallic, opaque, steel grey to silver white mineral with a relatively high specific gravity of 6.1....
provide nearly all the world's supply of arsenic

Arsenic

Arsenic is a well-known chemical element that has the symbol As and atomic number 33. Arsenic was first documented by Albertus Magnus in 1250....
as a byproduct of smelting

Smelting

Smelting is a form of extractive metallurgy; its main use is to produce a metal from its ore. This includes iron extraction from iron ore, and copper extraction and other base metals from their ores....
concentrates derived from these ore

Ore

An ore is a type of Rock that contains minerals such as gemstones and metals that can be extracted through mining and refined for use. Samples of ore in the form of exceptionally beautiful crystals, exotic layering visible when sectioned or polished or metallic presentations such as large nuggets or crystalline formations of metals suc...
s.

Realgar was also used by firework manufacturers to create the color white in fireworks prior to the availability of powdered metals such as Aluminum, 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, as well in the cores of some types of crackling stars.

Other traditional uses include manufacturing shot, printing and dyeing calico, and depilating and tanning hides. Realgar is very poisonous. It should be kept in good conditions such as a dark cool place. Wash hands after handling. Do not crush into powder.

Sources

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.

External links

American Mineralogist Vol 80, pp 400-403, 1995
American Mineralogist Vol 20, pp 1266-1274, 1992