Pararealgar
Encyclopedia
Pararealgar is an arsenic
sulfide mineral
with the chemical formula As4S4 also represented as AsS. It forms gradually from realgar
under exposure to light. Its name derives from the fact that its elemental composition is identical to realgar, As4S4. It is soft with a Mohs hardness of 1 - 1.5, is yellow orange in colour, and its monoclinic prismatic
crystals are very brittle, easily crumbling to powder.
It is one of the sulfide
s of arsenic and is one of two isomer
s of As4S4. It forms upon exposure of the symmetrical isomer to light. Its name derives from the fact that its elemental composition is identical to realgar, As4S4.
(As2S3), which is polymeric. In pararealgar, there are kinds of As centres (and three kinds of S centres). The molecule has Cs symmetry
. In realgar, the four As (and four S) centres are equivalent and the molecule has D2d symmetry. An analogous pair of isomers is also recognized for the corresponding phosphorus sulfide
s P4S4.
-bearing quartz
veins
typically as a result of exposure to light. It occurs associated with realgar, stibnite, tetrahedrite
, arsenopyrite
, duranusite, native arsenic
, arsenolite
, native sulfur, lepidocrocite
and pyrite
.
It was first described in 1980 for an occurrence in the Grey Rock Mine, Truax Creek, Bridge River area, Lillooet Mining Division, British Columbia
, Canada
. It has since been reported from a variety of locations worldwide.
Arsenic
Arsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.Arsenic is a metalloid...
sulfide mineral
Sulfide mineral
The sulfide minerals are a class of minerals containing sulfide as the major anion. Some sulfide minerals are economically important as metal ores. The sulfide class also includes the selenides, the tellurides, the arsenides, the antimonides, the bismuthinides, the sulfarsenides and the sulfosalts...
with the chemical formula As4S4 also represented as AsS. It forms gradually from realgar
Realgar
Realgar, α-As4S4, is an arsenic sulfide 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 colour, melts...
under exposure to light. Its name derives from the fact that its elemental composition is identical to realgar, As4S4. It is soft with a Mohs hardness of 1 - 1.5, is yellow orange in colour, and its monoclinic prismatic
Prism (geometry)
In geometry, a prism is a polyhedron with an n-sided polygonal base, a translated copy , and n other faces joining corresponding sides of the two bases. All cross-sections parallel to the base faces are the same. Prisms are named for their base, so a prism with a pentagonal base is called a...
crystals are very brittle, easily crumbling to powder.
It is one of the sulfide
Sulfide
A sulfide is an anion of sulfur in its lowest oxidation state of 2-. Sulfide is also a slightly archaic term for thioethers, a common type of organosulfur compound that are well known for their bad odors.- Properties :...
s of arsenic and is one of two isomer
Isomer
In chemistry, isomers are compounds with the same molecular formula but different structural formulas. Isomers do not necessarily share similar properties, unless they also have the same functional groups. There are many different classes of isomers, like stereoisomers, enantiomers, geometrical...
s of As4S4. It forms upon exposure of the symmetrical isomer to light. Its name derives from the fact that its elemental composition is identical to realgar, As4S4.
Structure
Both isomers of As4S4 are molecular, in contrast to the other main sulfide of arsenic, orpimentOrpiment
Orpiment, As2S3, is a common monoclinic arsenic sulfide mineral. It has a Mohs hardness of 1.5 to 2 and a specific gravity of 3.46. It melts at 300 °C to 325 °C...
(As2S3), which is polymeric. In pararealgar, there are kinds of As centres (and three kinds of S centres). The molecule has Cs symmetry
Symmetry group
The symmetry group of an object is the group of all isometries under which it is invariant with composition as the operation...
. In realgar, the four As (and four S) centres are equivalent and the molecule has D2d symmetry. An analogous pair of isomers is also recognized for the corresponding phosphorus sulfide
Phosphorus sulfide
The Phosphorus sulfides comprise a family of inorganic compounds containing only phosphorus and sulfur. These compounds have the formula P4Sx where x is less than or equal to 10...
s P4S4.
Occurrence
Pararealgar occurs as an alteration product of realgar in stibniteStibnite
Stibnite, sometimes called antimonite, is a sulfide mineral with the formula Sb2S3. This soft grey material crystallizes in an orthorhombic space group. It is the most important source for the metalloid antimony...
-bearing quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
veins
Vein (geology)
In geology, a vein is a distinct sheetlike body of crystallized minerals within a rock. Veins form when mineral constituents carried by an aqueous solution within the rock mass are deposited through precipitation...
typically as a result of exposure to light. It occurs associated with realgar, stibnite, tetrahedrite
Tetrahedrite
Tetrahedrite is a copper antimony sulfosalt mineral with formula: 12Sb4S13. It is the antimony endmember of the continuous solid solution series with arsenic bearing tennantite. Pure endmembers of the series are seldom if ever seen in nature. Of the two, the antimony rich phase is more common...
, 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. When dissolved in nitric acid, it releases elemental sulfur. When arsenopyrite is heated, it becomes magnetic and gives off toxic fumes...
, duranusite, native arsenic
Arsenic
Arsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.Arsenic is a metalloid...
, arsenolite
Arsenolite
Arsenolite is an arsenic mineral, chemical formula As2O3. It is formed as an oxidation product of arsenic sulfides. Commonly found as small octahedra it is white, but impurities of realgar or orpiment may give it a pink or yellow hue...
, native sulfur, lepidocrocite
Lepidocrocite
Lepidocrocite , also called esmeraldite or hydrohematite, is an iron oxide-hydroxide mineral. Lepidocrocite has an orthorhombic crystal structure, a hardness of 5, specific gravity of 4, a submetallic luster and a yellow-brown streak. It is red to reddish brown and forms when iron-containing...
and pyrite
Pyrite
The mineral pyrite, or iron pyrite, is an iron sulfide with the formula FeS2. This mineral's metallic luster and pale-to-normal, brass-yellow hue have earned it the nickname fool's gold because of its resemblance to gold...
.
It was first described in 1980 for an occurrence in the Grey Rock Mine, Truax Creek, Bridge River area, Lillooet Mining Division, British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
. It has since been reported from a variety of locations worldwide.