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Arsenopyrite ( IMA symbol: Apy) is an iron arsenic sulfide (FeAsS). It is a hard ( Mohs 5.5-6) metallic, opaque, steel grey to silver white mineral with a relatively high
Arsenopyrite crystallizes in the
Various transition group metals can substitute for iron in arsenopyrite. The arsenopyrite group includes the following rare minerals:
* Clinosafflorite:
* Gudmundite:
*
specific gravity
Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water at its dens ...
of 6.1. When dissolved in nitric acid
Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available ni ...
, it releases elemental sulfur. When arsenopyrite is heated, it produces sulfur and arsenic vapor. With 46% arsenic
Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, b ...
content, arsenopyrite, along with orpiment, is a principal ore of arsenic. When deposits of arsenopyrite become exposed to the atmosphere, the mineral slowly converts into iron arsenates. Arsenopyrite is generally an acid-consuming sulfide mineral, unlike iron pyrite
The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Fe S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral.
Pyrite's metallic luster and pale brass-yellow hue gi ...
which can lead to acid mine drainage.
The crystal habit, hardness, density, and garlic odour 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 is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile ...
. Consequently, it serves as an indicator of gold bearing reefs. Many arsenopyrite gold ores are refractory
In materials science, a refractory material or refractory is a material that is resistant to decomposition by heat, pressure, or chemical attack, and retains strength and form at high temperatures. Refractories are polycrystalline, polyphase, ...
, i.e. the gold is not easily cyanide leached from the mineral matrix.
Arsenopyrite is found in high temperature hydrothermal veins, in pegmatites, and in areas of contact metamorphism or metasomatism.
Crystallography
Arsenopyrite crystallizes in the monoclinic
In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic ...
crystal system and often shows prismatic crystal or columnar forms with striations and twinning 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 than pyrite. The ion description is imperfect because the material is semiconducting and the Fe-As and Fe-S bonds are highly covalent
A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atom ...
.Vaugn, D. J.; Craig, J. R. Mineral Chemistry of Metal Sulfides" Cambridge University Press, Cambridge: 1978. .
Related minerals
Various transition group metals can substitute for iron in arsenopyrite. The arsenopyrite group includes the following rare minerals:
* Clinosafflorite:
* Gudmundite:
*Glaucodot
Glaucodot is a cobalt iron arsenic sulfide mineral with formula . The cobalt:iron(II) ratio is typically 3:1 with minor nickel substituting. It forms a series with arsenopyrite . It is an opaque grey to tin-white typically found as massive forms w ...
or alloclasite Alloclasite () is a sulfosalt mineral ( IMA symbol: Acl). It is a member of the arsenopyrite group. Alloclasite crystallizes in the monoclinic system and typically forms as columnar to radiating acicular prismatic clusters. It is an opaque steel-gr ...
: or
* Iridarsenite:
* Osarsite or ruarsite: or
See also
* *Classification of minerals The classification of minerals is a process of determining to which of several groups minerals belong based on their chemical characteristics. Since the 1950s, this classification has been carried out by the International Mineralogical Association, ...
* List of minerals
References
External links
* {{Authority control Iron minerals Sulfide minerals Arsenic minerals Monoclinic minerals Minerals in space group 14