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Arsenopyrite

 
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Arsenopyrite is an iron arsenic 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...
 (FeAsS). It is a hard (Mohs
Mohs scale of mineral hardness

Not to be confused with Siemens_#Mho, a unit of electric conductance.The Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material....
 5.5-6) metallic, opaque, steel grey to silver white mineral with a relatively high 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 6.1. When dissolved in nitric acid
Nitric acid

Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosion and toxic strong acid that can cause severe burns....
, it releases elemental sulfur
Sulfur

Sulfur or sulphur is the chemical element that has the atomic number 16. It is denoted with the symbol S. It is an abundant Valence non-metal....
. When arsenopyrite is heated, it becomes magnetic and gives off toxic fumes. With 46% 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....
 content, arsenopyrite, 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....
, is a principal 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...
 of arsenic. When deposits of arsenopyrite become exposed to the atmosphere, usually due to mining, the mineral will slowly oxidize, converting the arsenic into oxides that are more soluble in water, leading to acid mine drainage
Acid mine drainage

Acid mine drainage , or acid rock drainage , refers to the outflow of acidic water from abandoned metal mining or coal mines. However, other areas where the earth has been disturbed may also contribute acid rock drainage to the environment....
.

The crystal habit, hardness, density, and garlic odor when struck are diagnostic.






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Arsenopyrite is an iron arsenic 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...
 (FeAsS). It is a hard (Mohs
Mohs scale of mineral hardness

Not to be confused with Siemens_#Mho, a unit of electric conductance.The Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material....
 5.5-6) metallic, opaque, steel grey to silver white mineral with a relatively high 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 6.1. When dissolved in nitric acid
Nitric acid

Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosion and toxic strong acid that can cause severe burns....
, it releases elemental sulfur
Sulfur

Sulfur or sulphur is the chemical element that has the atomic number 16. It is denoted with the symbol S. It is an abundant Valence non-metal....
. When arsenopyrite is heated, it becomes magnetic and gives off toxic fumes. With 46% 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....
 content, arsenopyrite, 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....
, is a principal 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...
 of arsenic. When deposits of arsenopyrite become exposed to the atmosphere, usually due to mining, the mineral will slowly oxidize, converting the arsenic into oxides that are more soluble in water, leading to acid mine drainage
Acid mine drainage

Acid mine drainage , or acid rock drainage , refers to the outflow of acidic water from abandoned metal mining or coal mines. However, other areas where the earth has been disturbed may also contribute acid rock drainage to the environment....
.

The crystal habit, hardness, density, and garlic odor when struck are diagnostic. Arsenopyrite in older literature may be referred to as mispickel, a name of German origin.

Arsenopyrite also can be associated with significant amounts of gold
Gold

Gold is a chemical element with the symbol Au and atomic number 79. It is a highly sought-after precious metal, having been used as money, as a store of value, in jewelry, in sculpture, and for ornamentation since the beginning of recorded history....
. Consequently it serves as an indicator of gold bearing reefs. Many arsenopyrite gold ores are refractory
Refractory

A refractory material is one that retains its strength at high temperatures. ASTM International C71 defines refractories as "non-metallic materials having those chemical and physical properties that made them applicable for structures, or as components of systems, that are exposed to environments above 1000 ?F "....
, i.e. the gold is not easily liberated from the mineral matrix.

Arsenopyrite is found in high temperature hydrothermal veins, in pegmatite
Pegmatite

Pegmatite is a very coarse-grained igneous rock that has a grain size of 20 mm or more; such rocks are referred to as pegmatitic.Most pegmatites are composed of quartz, feldspar and mica; in essence a "granite"....
s, and in areas of contact metamorphism
Metamorphism

Metamorphism is the solid-state Crystallization of pre-existing Rock due to changes in physical and chemical conditions, primarily heat, pressure, and the introduction of chemically active fluids....
 or metasomatism
Metasomatism

Metasomatism is the chemical alteration of a Rock by hydrothermal and other fluids.Metasomatism can occur via the action of hydrothermal fluids from an igneous or Metamorphism source....
.

Crystallography

Arsenopyrite crystallizes in the monoclinic crystal system
Crystal system

A crystal system is a category of space groups, which characterize symmetry of structures in three dimensions with translational symmetry in three directions, having a discrete class of Point groups in three dimensions....
 and often shows prismatic crystal or columnar forms with striation
Striation

Striations means a series of ridges, furrows or linear marks, and are used in several ways* Glacial striation* Striation , a striation as a result of a geological Fault ...
s and twinning
Crystal twinning

Crystal twinning occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals in a variety of specific configurations....
 common. Arsenopyrite may be referred to in older references as orthorhombic, but it has been shown to be monoclinic. In terms of its atomic structure, each Fe center is linked to three As atoms and three S atoms. The material can be described as Fe3+ with the diatomic trianion AsS3-. The connectivity of the atoms is more similar to that in marcasite
Marcasite

The mineral marcasite, sometimes called white iron pyrite, is iron sulfide . Marcasite is often mistakenly confused with pyrite, but marcasite is lighter and more brittle....
 than pyrite
Pyrite

The mineral pyrite, or iron pyrite, is an iron sulfide with the chemical formula ironsulfur2. This mineral's metallic Lustre and pale-to-normal, brass-yellow hue have earned it the nickname fool's gold due to its resemblance to gold....
. The ion description is imperfect because the material is semiconducting and the Fe-As and Fe-S bonds are highly covalent.

Related minerals

Various transition
Transition

Transition or transitional may refer to:* Transition * Transitional fossil* Transition * Transition metal* Transition state* Transition: an operation of a finite state machine...
 group metals can substitute for iron in arsenopyrite. The arsenopyrite group includes the following rare minerals:
  • Clinosafflorite: (Co,Fe,Ni)AsS
  • Gudmundite: FeSbS
  • Glaucodot
    Glaucodot

    Glaucodot is a cobalt iron arsenic sulfide mineral with formula: AsS. The cobalt:iron ratio is typically 3:1 with minor nickel substituting. It forms a series with arsenopyrite ....
     or alloclasite
    Alloclasite

    Alloclasite is a sulfosalt mineral. It is a member of the arsenopyrite group. Alloclasite crystallizes in the monoclinic system and typically forms as columnar to radiating acicular prismatic clusters....
    : (Fe,Co)AsS
  • Iridarsenite: (Ir,Ru)AsS
  • Osarsite or ruarsite: (Os,Ru)AsS or (Ru,Os)AsS