Iron(II) sulfide

Iron(II) sulfide

Overview
Iron sulfide or ferrous sulfide (Br.E. sulphide) is a chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 with the formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

 . In practice, iron sulfides are often non-stoichiometric. Powdered iron sulfide is pyrophoric (i.e. will ignite spontaneously in air).

"Iron sulfide" exists in several distinct forms, which differ in the ratio of sulfur to iron
Stoichiometry
Stoichiometry is a branch of chemistry that deals with the relative quantities of reactants and products in chemical reactions. In a balanced chemical reaction, the relations among quantities of reactants and products typically form a ratio of whole numbers...

 and properties:
  • Pyrrhotite
    Pyrrhotite
    Pyrrhotite is an unusual iron sulfide mineral with a variable iron content: FeS . The FeS endmember is known as troilite. Pyrrhotite is also called magnetic pyrite because the color is similar to pyrite and it is weakly magnetic...

    , Fe1-xS, a mineral, which displays ferrimagnetism
    Ferrimagnetism
    In physics, a ferrimagnetic material is one in which the magnetic moments of the atoms on different sublattices are opposed, as in antiferromagnetism; however, in ferrimagnetic materials, the opposing moments are unequal and a spontaneous magnetization remains...

     and crystallizes in monoclinic system.
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Encyclopedia
Iron sulfide or ferrous sulfide (Br.E. sulphide) is a chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 with the formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

 . In practice, iron sulfides are often non-stoichiometric. Powdered iron sulfide is pyrophoric (i.e. will ignite spontaneously in air).

Forms of iron sulfide


"Iron sulfide" exists in several distinct forms, which differ in the ratio of sulfur to iron
Stoichiometry
Stoichiometry is a branch of chemistry that deals with the relative quantities of reactants and products in chemical reactions. In a balanced chemical reaction, the relations among quantities of reactants and products typically form a ratio of whole numbers...

 and properties:
  • Pyrrhotite
    Pyrrhotite
    Pyrrhotite is an unusual iron sulfide mineral with a variable iron content: FeS . The FeS endmember is known as troilite. Pyrrhotite is also called magnetic pyrite because the color is similar to pyrite and it is weakly magnetic...

    , Fe1-xS, a mineral, which displays ferrimagnetism
    Ferrimagnetism
    In physics, a ferrimagnetic material is one in which the magnetic moments of the atoms on different sublattices are opposed, as in antiferromagnetism; however, in ferrimagnetic materials, the opposing moments are unequal and a spontaneous magnetization remains...

     and crystallizes in monoclinic system. Iron metal shows ferromagnetism
    Ferromagnetism
    Ferromagnetism is the basic mechanism by which certain materials form permanent magnets, or are attracted to magnets. In physics, several different types of magnetism are distinguished...

    ; iron sulfides do not.
  • Troilite
    Troilite
    Troilite is a rare iron sulfide mineral with the simple formula of FeS. It is the iron rich endmember of the pyrrhotite group. Pyrrhotite has the formula FeS which is iron deficient...

    , FeS, a stoichiometric compound that adopts hexagonal symmetry.
  • Mackinawite
    Mackinawite
    Mackinawite is an iron nickel sulfide mineral with formula 1 + xS . It crystallizes in the tetragonal crystal system and occurs as opaque bronze to grey-white tabular crystals and anhedral masses. It has a Mohs hardness of 2.5 and a specific gravity of 4.17.-Occurrence:It occurs in serpentinized...

    , Fe1+xS the least stable form of iron sulfide; mackinawite has a layered structure.
  • 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...

     and marcasite
    Marcasite
    The mineral marcasite, sometimes called white iron pyrite, is iron sulfide with orthorhombic crystal structure. It is physically and crystallographically distinct from pyrite, which is iron sulfide with cubic crystal structure. Both structures do have in common that they contain the disulfide...

    , which are diamagnetic minerals, have the formula FeS2.
  • Greigite
    Greigite
    Greigite is an iron sulfide mineral with formula Fe3S4. It is the sulfur equivalent of the iron oxide magnetite . It was first described in 1964 for an occurrence in San Bernardino County, California, and named after the mineralogist and physical chemist Joseph W...

     (Fe3S4) a ferromagnetic species akin to magnetite
    Magnetite
    Magnetite is a ferrimagnetic mineral with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. The chemical IUPAC name is iron oxide and the common chemical name is ferrous-ferric oxide. The formula for magnetite may also be written as FeO·Fe2O3, which is one part...

     (Fe3O4).

Chemical reactions


Iron sulfide reacts with hydrochloric acid
Hydrochloric acid
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....

, releasing the pungent and very toxic hydrogen sulfide
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...

FeS + 2 HCl → FeCl2 + H2S

FeS can be obtained by the heating of iron and sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

:
Fe + S → FeS

Biology and biochemistry



As organic matter decays under low-oxygen (or hypoxic
Hypoxia (environmental)
Hypoxia, or oxygen depletion, is a phenomenon that occurs in aquatic environments as dissolved oxygen becomes reduced in concentration to a point where it becomes detrimental to aquatic organisms living in the system...

) conditions such as in swamps or dead zones
Dead zone (ecology)
Dead zones are hypoxic areas in the world's oceans, the observed incidences of which have been increasing since oceanographers began noting them in the 1970s. These occur near inhabited coastlines, where aquatic life is most concentrated...

 of lakes and oceans, sulfate-reducing bacteria
Sulfate-reducing bacteria
Sulfate-reducing bacteria are those bacteria and archaea that can obtain energy by oxidizing organic compounds or molecular hydrogen while reducing sulfate to hydrogen sulfide...

 will use the sulfate
Sulfate
In inorganic chemistry, a sulfate is a salt of sulfuric acid.-Chemical properties:...

s present in the water to oxidize the organic matter, producing hydrogen sulfide
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...

 as waste. Some of the hydrogen sulfide will react with metal ions in the water to produce metal sulfides, which are not water soluble. These metal sulfides, such as iron(II) sulfide, are often black or brown, leading to the color of sludge.

Pyrrotite is a waste product of the Desulfovibrio
Desulfovibrionales
The Desulfovibrionales are an order of Proteobacteria, with four families. Like all Proteobacteria, they are gram-negative. The majority are sulfate-reducing, with the exception of Lawsonia and Bilophila. All members of this order are strictly anaerobic. Most species are mesophilic, there are also...

bacteria, a sulfate reducing bacteria.

When eggs are cooked for a long time, the yolk's surface may turn green. This is due to iron(II) sulfide which forms as iron from the yolk meets hydrogen sulfide released from the egg white by the heat. This reaction occurs more rapidly in older eggs as the whites are more alkaline.

The presence of ferrous sulfide as a visible black precipitate in the growth medium
Growth medium
A growth medium or culture medium is a liquid or gel designed to support the growth of microorganisms or cells, or small plants like the moss Physcomitrella patens.There are different types of media for growing different types of cells....

 peptone iron agar can be used to distinguish between microorganisms that produce the cysteine metabolizing
Cysteine metabolism
Cysteine metabolism refers to the biological pathways that consume or create cysteine. The pathways of different amino acids and other metabolites interweave and overlap to creating complex systems.-Human cysteine metabolism:...

 enzyme cysteine desulfhydrase
D-cysteine desulfhydrase
In enzymology, a D-cysteine desulfhydrase is an enzyme that catalyzes the chemical reactionThus, the two substrates of this enzyme are D-cysteine and H2O, whereas its 3 products are sulfide, NH3, and pyruvate....

 and those that do not. Peptone iron agar contains the amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...

 cysteine
Cysteine
Cysteine is an α-amino acid with the chemical formula HO2CCHCH2SH. It is a non-essential amino acid, which means that it is biosynthesized in humans. Its codons are UGU and UGC. The side chain on cysteine is thiol, which is polar and thus cysteine is usually classified as a hydrophilic amino acid...

 and a chemical indicator, ferric citrate
Ammonium ferric citrate
Ammonium ferric citrate is a food additive with E number E381 used as an acidity regulator. It is a green or reddish-brown powder which is very soluble in water....

. The degradation of cysteine releases hydrogen sulfide
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...

 gas that reacts with the ferric
Ferric
Ferric refers to iron-containing materials or compounds. In chemistry the term is reserved for iron with an oxidation number of +3, also denoted iron or Fe3+. On the other hand, ferrous refers to iron with oxidation number of +2, denoted iron or Fe2+...

 citrate
Citrate
A citrate can refer either to the conjugate base of citric acid, , or to the esters of citric acid. An example of the former, a salt is trisodium citrate; an ester is triethyl citrate.-Other citric acid ions:...

to produce ferrous sulfide.