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mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...
pyrite (), or iron pyrite, also known as fool's gold, is an
iron sulfide Iron sulfide or Iron sulphide can refer to range of chemical compounds composed of iron and sulfur. Minerals By increasing order of stability: * Iron(II) sulfide, FeS * Greigite, Fe3S4 (cubic) * Pyrrhotite, Fe1−xS (where x = 0 to 0.2) (mono ...
with the
chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...
Fe S2 (iron (II) disulfide). Pyrite is the most abundant
sulfide mineral The sulfide minerals are a class of minerals containing sulfide (S2−) or disulfide (S22−) as the major anion. Some sulfide minerals are economically important as metal ores. The sulfide class also includes the selenides, the tellurides, th ...
. Pyrite's metallic luster and pale brass-yellow
hue In color theory, hue is one of the main properties (called color appearance parameters) of a color, defined technically in the CIECAM02 model as "the degree to which a stimulus can be described as similar to or different from stimuli that ...
give it a superficial resemblance to
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 ...
, hence the well-known nickname of ''fool's gold''. The color has also led to the nicknames ''brass'', ''brazzle'', and ''Brazil'', primarily used to refer to pyrite found in
coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when ...
. The name ''pyrite'' is derived from the
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
(), 'stone or mineral which strikes fire', in turn from (), 'fire'. In ancient Roman times, this name was applied to several types of stone that would create sparks when struck against
steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistan ...
;
Pliny the Elder Gaius Plinius Secundus (AD 23/2479), called Pliny the Elder (), was a Roman author, naturalist and natural philosopher, and naval and army commander of the early Roman Empire, and a friend of the emperor Vespasian. He wrote the encyclopedic ' ...
described one of them as being brassy, almost certainly a reference to what we now call pyrite. By
Georgius Agricola Georgius Agricola (; born Georg Pawer or Georg Bauer; 24 March 1494 – 21 November 1555) was a German Humanist scholar, mineralogist and metallurgist. Born in the small town of Glauchau, in the Electorate of Saxony of the Holy Roman Empire ...
's time, , the term had become a generic term for all of the
sulfide minerals The sulfide minerals are a class of minerals containing sulfide (S2−) or disulfide (S22−) as the major anion. Some sulfide minerals are economically important as metal ores. The sulfide class also includes the selenides, the tellurides, ...
. Pyrite is usually found associated with other sulfides or
oxide An oxide () is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the E ...
s in
quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical f ...
veins Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated ...
,
sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...
, and
metamorphic rock Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, caus ...
, as well as in coal beds and as a replacement mineral in
fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
s, but has also been identified in the
sclerite A sclerite (Greek , ', meaning " hard") is a hardened body part. In various branches of biology the term is applied to various structures, but not as a rule to vertebrate anatomical features such as bones and teeth. Instead it refers most commonly ...
s of scaly-foot gastropods. Despite being nicknamed fool's gold, pyrite is sometimes found in association with small quantities of gold. A substantial proportion of the gold is "invisible gold" incorporated into the pyrite (see Carlin-type gold deposit). It has been suggested that the presence of both gold and
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 ...
is a case of
coupled substitution Coupled substitution is the geological process by which two elements simultaneous substitute into a crystal in order to maintain overall electrical neutrality and keep the charge constant. In forming a solid solution series, ionic size is more ...
but as of 1997 the chemical state of the gold remained controversial.


Uses

Pyrite enjoyed brief popularity in the 16th and 17th centuries as a source of
ignition Ignition may refer to: Science and technology * Firelighting, the human act of creating a fire for warmth, cooking and other uses * Combustion, an exothermic chemical reaction between a fuel and an oxidant * Fusion ignition, the point at which a ...
in early
firearm A firearm is any type of gun designed to be readily carried and used by an individual. The term is legally defined further in different countries (see Legal definitions). The first firearms originated in 10th-century China, when bamboo tubes ...
s, most notably the
wheellock A wheellock, wheel-lock or wheel lock is a friction-wheel mechanism which creates a spark that causes a firearm to fire. It was the next major development in firearms technology after the matchlock and the first self-igniting firearm. Its name is ...
, where a sample of pyrite was placed against a circular file to strike the sparks needed to fire the gun. Pyrite is used with
flint Flint, occasionally flintstone, is a sedimentary cryptocrystalline form of the mineral quartz, categorized as the variety of chert that occurs in chalk or marly limestone. Flint was widely used historically to make stone tools and start ...
stone and a form of
tinder Tinder is easily combustible material used to start a fire. Tinder is a finely divided, open material which will begin to glow under a shower of sparks. Air is gently wafted over the glowing tinder until it bursts into flame. The flaming tinder i ...
made of
stringybark A stringybark can be any of the many ''Eucalyptus'' species which have thick, fibrous bark. Like all eucalypts, stringybarks belong to the family Myrtaceae. In exceptionally fertile locations some stringybark species (in particular messmate strin ...
by the Kaurna people, people of
South Australia South Australia (commonly abbreviated as SA) is a States and territories of Australia, state in the southern central part of Australia. It covers some of the most arid parts of the country. With a total land area of , it is the fourth-largest o ...
, as a traditional method of starting fires. Pyrite has been used since classical times to manufacture ''copperas'' (
ferrous sulfate Iron(II) sulfate (British English: iron(II) sulphate) or ferrous sulfate denotes a range of salts with the formula Fe SO4·''x''H2O. These compounds exist most commonly as the hepta hydrate (''x'' = 7) but several values for x are kn ...
). Iron pyrite was heaped up and allowed to weather (an example of an early form of heap leaching). The acidic runoff from the heap was then boiled with iron to produce iron sulfate. In the 15th century, new methods of such leaching began to replace the burning of sulfur as a source of
sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular fo ...
. By the 19th century, it had become the dominant method. Pyrite remains in commercial use for the production of
sulfur dioxide Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic a ...
, for use in such applications as the
paper industry The pulp and paper industry comprises companies that use wood as raw material and produce pulp, paper, paperboard and other cellulose-based products. Manufacturing process The pulp is fed to a paper machine where it is formed as a paper web a ...
, and in the manufacture of sulfuric acid. Thermal decomposition of pyrite into FeS (
iron(II) sulfide Iron(II) sulfide or ferrous sulfide (Br.E. sulphide) is one of a family chemical compounds and minerals with the approximate formula . Iron sulfides are often iron-deficient non-stoichiometric. All are black, water-insoluble solids. Preparatio ...
) and elemental sulfur starts at ; at around , ''p''S2 is about . A newer commercial use for pyrite is as the
cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in whi ...
material in
Energizer Energizer Holdings, Inc. is an American manufacturer and one of the world's largest manufacturers of batteries, headquartered in St. Louis, Missouri. It produces batteries under the Energizer, Ray-O-Vac, Varta, and Eveready brand names, and for ...
brand non-rechargeable lithium metal batteries. Pyrite is a
semiconductor material A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. ...
with a
band gap In solid-state physics, a band gap, also called an energy gap, is an energy range in a solid where no electronic states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference ( ...
of 0.95 eV. Pure pyrite is naturally n-type, in both crystal and thin-film forms, potentially due to sulfur vacancies in the pyrite crystal structure acting as n-dopants. During the early years of the 20th century, pyrite was used as a mineral detector in
radio Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30  hertz (Hz) and 300  gigahertz (GHz). They are generated by an electronic device called a tr ...
receivers, and is still used by
crystal radio A crystal radio receiver, also called a crystal set, is a simple radio receiver, popular in the early days of radio. It uses only the power of the received radio signal to produce sound, needing no external power. It is named for its most imp ...
hobbyists. Until the
vacuum tube A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied. The type known as ...
matured, the crystal detector was the most sensitive and dependable
detector A sensor is a device that produces an output signal for the purpose of sensing a physical phenomenon. In the broadest definition, a sensor is a device, module, machine, or subsystem that detects events or changes in its environment and sends ...
available—with considerable variation between mineral types and even individual samples within a particular type of mineral. Pyrite detectors occupied a midway point between
galena Galena, also called lead glance, is the natural mineral form of lead(II) sulfide (PbS). It is the most important ore of lead and an important source of silver. Galena is one of the most abundant and widely distributed sulfide minerals. It cr ...
detectors and the more mechanically complicated perikon mineral pairs. Pyrite detectors can be as sensitive as a modern 1N34A
germanium Germanium is a chemical element with the symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid in the carbon group that is chemically similar to its group neighbors ...
diode A diode is a two-terminal electronic component that conducts current primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other. A diod ...
detector. Pyrite has been proposed as an abundant, non-toxic, inexpensive material in low-cost
photovoltaic Photovoltaics (PV) is the conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect, a phenomenon studied in physics, photochemistry, and electrochemistry. The photovoltaic effect is commercially ...
solar panels. Synthetic iron sulfide was used with
copper sulfide Copper sulfides describe a family of chemical compounds and minerals with the formula CuxSy. Both minerals and synthetic materials comprise these compounds. Some copper sulfides are economically important ores. Prominent copper sulfide mineral ...
to create the photovoltaic material. More recent efforts are working toward thin-film solar cells made entirely of pyrite. Pyrite is used to make
marcasite jewelry Marcasite jewellery is jewellery made using cut and polished pieces of pyrite (fool's gold) as gemstone, and not, as the name suggests, from marcasite. Both pyrite and marcasite are chemically iron sulphide, but differ in their crystal structur ...
. Marcasite jewelry, made from small faceted pieces of pyrite, often set in
silver Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical ...
, was known since ancient times and was popular in the
Victorian era In the history of the United Kingdom and the British Empire, the Victorian era was the period of Queen Victoria's reign, from 20 June 1837 until her death on 22 January 1901. The era followed the Georgian period and preceded the Edwa ...
. At the time when the term became common in jewelry making, "marcasite" referred to all iron sulfides including pyrite, and not to the orthorhombic FeS2 mineral
marcasite The mineral marcasite, sometimes called “white iron pyrite”, is iron sulfide (FeS2) with orthorhombic crystal structure. It is physically and crystallographically distinct from pyrite, which is iron sulfide with cubic crystal structure. Both ...
which is lighter in color, brittle and chemically unstable, and thus not suitable for jewelry making. Marcasite jewelry does not actually contain the mineral marcasite. The specimens of pyrite, when it appears as good quality crystals, are used in decoration. They are also very popular in mineral collecting. Among the sites that provide the best specimens are Soria and La Rioja provinces (Spain). In value terms,
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
($47 million) constitutes the largest market for imported unroasted iron pyrites worldwide, making up 65% of global imports. China is also the fastest growing in terms of the unroasted iron pyrites imports, with a
CAGR Compound annual growth rate (CAGR) is a business and investing specific term for the geometric progression ratio that provides a constant rate of return over the time period. CAGR is not an accounting term, but it is often used to describe some ele ...
of +27.8% from 2007 to 2016.


Research

In July 2020 scientists reported that they have observed a voltage-induced transformation of normally
diamagnetic Diamagnetic materials are repelled by a magnetic field; an applied magnetic field creates an induced magnetic field in them in the opposite direction, causing a repulsive force. In contrast, paramagnetic and ferromagnetic materials are attracted ...
pyrite into a
ferromagnetic Ferromagnetism is a property of certain materials (such as iron) which results in a large observed magnetic permeability, and in many cases a large magnetic coercivity allowing the material to form a permanent magnet. Ferromagnetic materials ...
material, which may lead to applications in devices such as solar cells or magnetic data storage. Researchers at Trinity College Dublin, Ireland have demonstrated that FeS2 can be exfoliated into few-layers just like other two-dimensional layered materials such as graphene by a simple liquid-phase exfoliation route. This is the first study to demonstrate the production of non-layered 2D-platelets from 3D bulk FeS2. Furthermore, they have used these 2D-platelets with 20% single walled carbon-nanotube as an anode material in lithium-ion batteries, reaching a capacity of 1000 mAh/g close to the theoretical capacity of FeS2. In 2021,a natural pyrite stone has been crushed and pre-treated followed by liquid-phase exfoliation into two-dimensional nanosheets, which has shown capacities of 1200 mAh/g as an anode in lithium-ion batteries.


Formal oxidation states for pyrite, marcasite, molybdenite and arsenopyrite

From the perspective of classical
inorganic chemistry Inorganic chemistry deals with synthesis and behavior of inorganic and organometallic compounds. This field covers chemical compounds that are not carbon-based, which are the subjects of organic chemistry. The distinction between the two disci ...
, which assigns formal oxidation states to each atom, pyrite and marcasite are probably best described as Fe2+ 2sup>2−. This formalism recognizes that the sulfur atoms in pyrite occur in pairs with clear S–S bonds. These
persulfide In chemistry, persulfide refers to the functional group R-S-S-H. Persulfides are intermediates in the biosynthesis of iron-sulfur proteins and are invoked as precursors to hydrogen sulfide, a signaling molecule. Nomenclature The nomenclature use ...
sup>–S–Sunits can be viewed as derived from hydrogen disulfide, H2S2. Thus pyrite would be more descriptively called iron persulfide, not iron disulfide. In contrast,
molybdenite Molybdenite is a mineral of molybdenum disulfide, Mo S2. Similar in appearance and feel to graphite, molybdenite has a lubricating effect that is a consequence of its layered structure. The atomic structure consists of a sheet of molybdenum ato ...
, MoS2, features isolated sulfide S2− centers and the oxidation state of molybdenum is Mo4+. The mineral
arsenopyrite 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 specific gravity of 6.1. When dissolved in nitric acid, it releases elem ...
has the formula Fe AsS. Whereas pyrite has 2sup>2– units, arsenopyrite has sSsup>3– units, formally derived from
deprotonation Deprotonation (or dehydronation) is the removal (transfer) of a proton (or hydron, or hydrogen cation), (H+) from a Brønsted–Lowry acid in an acid–base reaction.Henry Jakubowski, Biochemistry Online Chapter 2A3, https://employees.csbsju. ...
of arsenothiol (H2AsSH). Analysis of classical oxidation states would recommend the description of arsenopyrite as Fe3+ sSsup>3−.


Crystallography

Iron-pyrite FeS2 represents the prototype compound of the
crystallographic Crystallography is the experimental science of determining the arrangement of atoms in crystalline solids. Crystallography is a fundamental subject in the fields of materials science and solid-state physics (condensed matter physics). The wor ...
pyrite structure. The structure is simple cubic and was among the first
crystal structures A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macrosc ...
solved by
X-ray diffraction X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...
. It belongs to the crystallographic
space group In mathematics, physics and chemistry, a space group is the symmetry group of an object in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of an object that leave it uncha ...
''Pa'' and is denoted by the Strukturbericht notation C2. Under thermodynamic standard conditions the
lattice constant A lattice constant or lattice parameter is one of the physical dimensions and angles that determine the geometry of the unit cells in a crystal lattice, and is proportional to the distance between atoms in the crystal. A simple cubic crystal has o ...
a of stoichiometric iron pyrite FeS2 amounts to . The
unit cell In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector, for example) does not necessaril ...
is composed of a Fe face-centered cubic sublattice into which the ions are embedded. (Note though that the iron atoms in the faces are not equivalent by translation alone to the iron atoms at the corners.) The pyrite structure is also seen in other ''MX''2 compounds of
transition metals In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. They are the elements that ca ...
''M'' and
chalcogen The chalcogens (ore forming) ( ) are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family. Group 16 consists of the elements oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and the radioac ...
s ''X'' = O, S, Se and Te. Certain dipnictides with ''X'' standing for P, As and Sb etc. are also known to adopt the pyrite structure. The Fe atoms are bonded to six S atoms, giving a distorted octahedron. The material is a
semiconductor A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way ...
. The Fe ions is usually considered to be '' low spin''
divalent In chemistry, the valence (US spelling) or valency (British spelling) of an chemical element, element is the measure of its combining capacity with other atoms when it forms chemical compounds or molecules. Description The combining capacity, ...
state (as shown by
Mössbauer spectroscopy Mössbauer spectroscopy is a spectroscopic technique based on the Mössbauer effect. This effect, discovered by Rudolf Mössbauer (sometimes written "Moessbauer", German: "Mößbauer") in 1958, consists of the nearly recoil-free emission and abs ...
as well as XPS). The material as a whole behaves as a Van Vleck
paramagnet Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, d ...
, despite its low-spin divalency. The sulfur centers occur in pairs, described as S22−. Reduction of pyrite with potassium gives
potassium dithioferrate Potassium dithioferrate is the inorganic compound with the formula KFeS2. It is a purple solid that is insoluble in water. Regarding its chemical structure, the compound consists of infinite chains of edge-shared anionic FeS4 tetrahedra. Associate ...
, KFeS2. This material features ferric ions and isolated sulfide (S2-) centers. The S atoms are tetrahedral, being bonded to three Fe centers and one other S atom. The site symmetry at Fe and S positions is accounted for by point symmetry groups ''C''3''i'' and ''C''3, respectively. The missing center of inversion at S lattice sites has important consequences for the crystallographic and physical properties of iron pyrite. These consequences derive from the crystal electric field active at the sulfur lattice site, which causes a polarisation of S ions in the pyrite lattice. The polarisation can be calculated on the basis of higher-order
Madelung constant The Madelung constant is used in determining the electrostatic potential of a single ion in a crystal by approximating the ions by point charges. It is named after Erwin Madelung, a German physicist. Because the anions and cations in an ionic sol ...
s and has to be included in the calculation of the
lattice energy In chemistry, the lattice energy is the energy change upon formation of one mole of a crystalline ionic compound from its constituent ions, which are assumed to initially be in the gaseous state. It is a measure of the cohesive forces that bin ...
by using a generalised
Born–Haber cycle The Born–Haber cycle is an approach to analyze reaction energies. It was named after the two German scientists Max Born and Fritz Haber, who developed it in 1919. It was also independently formulated by Kasimir Fajans and published concurrentl ...
. This reflects the fact that the covalent bond in the sulfur pair is inadequately accounted for by a strictly ionic treatment. Arsenopyrite has a related structure with heteroatomic As–S pairs rather than S-S pairs. Marcasite also possesses homoatomic anion pairs, but the arrangement of the metal and diatomic anions differ from that of pyrite. Despite its name, chalcopyrite () does not contain dianion pairs, but single S2− sulfide anions.


Crystal habit

Pyrite usually forms cuboid crystals, sometimes forming in close association to form raspberry-shaped masses called framboids. However, under certain circumstances, it can form
anastomosing An anastomosis (, plural anastomoses) is a connection or opening between two things (especially cavities or passages) that are normally diverging or branching, such as between blood vessels, leaf veins, or streams. Such a connection may be normal ...
filaments or T-shaped crystals. Pyrite can also form shapes almost the same as a regular
dodecahedron In geometry, a dodecahedron (Greek , from ''dōdeka'' "twelve" + ''hédra'' "base", "seat" or "face") or duodecahedron is any polyhedron with twelve flat faces. The most familiar dodecahedron is the regular dodecahedron with regular pentagon ...
, known as pyritohedra, and this suggests an explanation for the artificial geometrical models found in Europe as early as the 5th century BC.


Varieties

Cattierite Cattierite (CoS2) is a cobalt sulfide mineral found in the Democratic Republic of Congo. It was discovered together with the nickel sulfide vaesite by Johannes F. Vaes, a Belgian mineralologist and named after Felicien Cattier, who was chairman of ...
( Co S2),
vaesite Vaesite ( Ni S2) is a mineral found together with cattierite in the Democratic Republic of Congo. It is named after Johannes F. Vaes, a Belgian mineralologist. It is part of the pyrite group The pyrite group of minerals is a set of cubic crystal ...
( Ni S2) and
hauerite Hauerite is a manganese sulfide mineral with the chemical formula Mn S2. It forms reddish brown or black octahedral crystals with the pyrite structure and it is usually found associated with the sulfides of other transition metals such as ramber ...
( Mn S2), as well as
sperrylite Sperrylite is a platinum arsenide mineral with the chemical formula and is an opaque metallic tin white mineral which crystallizes in the isometric system with the pyrite group structure. It forms cubic, octahedral or pyritohedral crystals in ...
( Pt As2) are similar in their structure and belong also to the pyrite group. is a nickel-cobalt bearing variety of pyrite, with > 50% substitution of Ni2+ for Fe2+ within pyrite. Bravoite is not a formally recognised mineral, and is named after the Peruvian scientist Jose J. Bravo (1874–1928).


Distinguishing similar minerals

Pyrite is distinguishable from
native 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 meta ...
by its hardness, brittleness and crystal form. Pyrite fractures are very uneven, sometimes
conchoidal Conchoidal fracture describes the way that brittle materials break or fracture when they do not follow any natural planes of separation. Mindat.org defines conchoidal fracture as follows: "a fracture with smooth, curved surfaces, typically slig ...
because it does not cleave along a preferential plane. Native
gold nugget :''"Gold nugget" may also refer to the catfish Baryancistrus xanthellus or the mango cultivar Gold Nugget.'' A gold nugget is a naturally occurring piece of native gold. Watercourses often concentrate nuggets and finer gold in placers. Nuggets ...
s, or glitters, do not break but deform in a
ductile Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile stres ...
way. Pyrite is brittle, gold is malleable. Natural gold tends to be anhedral (irregularly shaped without well defined faces), whereas pyrite comes as either cubes or multifaceted crystals with well developed and sharp faces easy to recognise. Well crystallised pyrite crystals are
euhedral Euhedral crystals (also known as idiomorphic or automorphic crystals) are those that are well-formed, with sharp, easily recognised faces. The opposite is anhedral (also known as '' xenomorphic'' or ''allotriomorphic''): a rock with an anhedr ...
(''i.e.'', with nice faces). Pyrite can often be distinguished by the striations which, in many cases, can be seen on its surface.
Chalcopyrite Chalcopyrite ( ) is a copper iron sulfide mineral and the most abundant copper ore mineral. It has the chemical formula CuFeS2 and crystallizes in the tetragonal system. It has a brassy to golden yellow color and a hardness of 3.5 to 4 on the Mo ...
() is brighter yellow with a greenish hue when wet and is softer (3.5–4 on Mohs' scale).
Arsenopyrite 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 specific gravity of 6.1. When dissolved in nitric acid, it releases elem ...
(FeAsS) is silver white and does not become more yellow when wet.


Hazards

Iron pyrite is unstable when exposed to the
oxidizing Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...
conditions prevailing at the Earth's surface: iron pyrite in contact with atmospheric
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
and water, or damp, ultimately decomposes into iron oxyhydroxides (
ferrihydrite Ferrihydrite (Fh) is a widespread hydrous ferric oxyhydroxide mineral at the Earth's surface, and a likely constituent in extraterrestrial materials. It forms in several types of environments, from freshwater to marine systems, aquifers to hy ...
, FeO(OH)) and
sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular fo ...
(). This process is accelerated by the action of ''
Acidithiobacillus ''Acidithiobacillus'' is a genus of the ''Acidithiobacillia'' in the " Pseudomonadota". The genus includes acidophilic organisms capable of iron and/or sulfur oxidation. Like all ''"Pseudomonadota"'', ''Acidithiobacillus'' spp. are Gram-negative ...
'' bacteria which oxidize pyrite to first produce
ferrous ion In chemistry, the adjective Ferrous indicates a compound that contains iron(II), meaning iron in its +2 oxidation state, possibly as the divalent cation Fe2+. It is opposed to "ferric" or iron(III), meaning iron in its +3 oxidation state, such a ...
s (),
sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...
ions (), and release protons (, or ). In a second step, the ferrous ions () are oxidized by into
ferric ion In chemistry, iron(III) refers to the element iron in its +3 oxidation state. In ionic compounds (salts), such an atom may occur as a separate cation (positive ion) denoted by Fe3+. The adjective ferric or the prefix ferri- is often used to sp ...
s () which
hydrolyze Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolysis i ...
also releasing ions and producing FeO(OH). These oxidation reactions occur more rapidly when pyrite is finely dispersed (framboidal crystals initially formed by
sulfate reducing bacteria Sulfate-reducing microorganisms (SRM) or sulfate-reducing prokaryotes (SRP) are a group composed of sulfate-reducing bacteria (SRB) and sulfate-reducing archaea (SRA), both of which can perform anaerobic respiration utilizing sulfate () as termina ...
(SRB) in argillaceous sediments or dust from mining operations).


Pyrite oxidation and acid mine drainage

Pyrite oxidation by atmospheric in the presence of moisture () initially produces ferrous ions () and
sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular fo ...
which dissociates into
sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...
ions and
protons A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron m ...
, leading to
acid mine drainage Acid mine drainage, acid and metalliferous drainage (AMD), or acid rock drainage (ARD) is the outflow of acidic water from metal mines or coal mines. Acid rock drainage occurs naturally within some environments as part of the rock weathering ...
(AMD). An example of acid rock drainage caused by pyrite is the
2015 Gold King Mine waste water spill The 2015 Gold King Mine waste water spill was an environmental disaster that began at the Gold King Mine near Silverton, Colorado, when Environmental Protection Agency (EPA) personnel, along with workers for Environmental Restoration LLC (a Mis ...
. :2FeS2 + 7O2 + 2H2O -> 2Fe^ + 4SO4^ + 4H+.


Dust explosions

Pyrite oxidation is sufficiently
exothermic In thermodynamics, an exothermic process () is a thermodynamic process or reaction that releases energy from the system to its surroundings, usually in the form of heat, but also in a form of light (e.g. a spark, flame, or flash), electricity ...
that underground
coal mine Coal mining is the process of extracting coal from the ground. Coal is valued for its energy content and since the 1880s has been widely used to generate electricity. Steel and cement industries use coal as a fuel for extraction of iron from ...
s in high-sulfur coal seams have occasionally had serious problems with
spontaneous combustion Spontaneous combustion or spontaneous ignition is a type of combustion which occurs by self-heating (increase in temperature due to exothermic internal reactions), followed by thermal runaway (self heating which rapidly accelerates to high te ...
. The solution is the use of buffer blasting and the use of various sealing or cladding agents to hermetically seal the mined-out areas to exclude oxygen. In modern coal mines,
limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms w ...
dust is sprayed onto the exposed coal surfaces to reduce the hazard of
dust explosion A dust explosion is the rapid combustion of fine particles suspended in the air within an enclosed location. Dust explosions can occur where any dispersed powdered combustible material is present in high-enough concentrations in the atmosphere o ...
s. This has the secondary benefit of neutralizing the acid released by pyrite oxidation and therefore slowing the oxidation cycle described above, thus reducing the likelihood of spontaneous combustion. In the long term, however, oxidation continues, and the
hydrated Drinking is the act of ingesting water or other liquids into the body through the mouth, proboscis, or elsewhere. Humans drink by swallowing, completed by peristalsis in the esophagus. The physiological processes of drinking vary widely among o ...
sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...
s formed may exert crystallization pressure that can expand cracks in the rock and lead eventually to roof fall.


Weakened building materials

Building stone containing pyrite tends to stain brown as pyrite oxidizes. This problem appears to be significantly worse if any
marcasite The mineral marcasite, sometimes called “white iron pyrite”, is iron sulfide (FeS2) with orthorhombic crystal structure. It is physically and crystallographically distinct from pyrite, which is iron sulfide with cubic crystal structure. Both ...
is present. The presence of pyrite in the
aggregate Aggregate or aggregates may refer to: Computing and mathematics * collection of objects that are bound together by a root entity, otherwise known as an aggregate root. The aggregate root guarantees the consistency of changes being made within the ...
used to make
concrete Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wid ...
can lead to severe deterioration as pyrite oxidizes. In early 2009, problems with
Chinese drywall "Chinese drywall" refers to an environmental health issue involving defective drywall manufactured in China, imported to the United States and used in residential construction between 2001 and 2009 affecting "an estimated 100,000 homes in more tha ...
imported into the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...
after
Hurricane Katrina Hurricane Katrina was a destructive Category 5 Atlantic hurricane that caused over 1,800 fatalities and $125 billion in damage in late August 2005, especially in the city of New Orleans and the surrounding areas. It was at the time the cost ...
were attributed to pyrite oxidation, followed by microbial sulfate reduction which released
hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The under ...
gas (). These problems included a foul odor and
corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engi ...
of
copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pink ...
wiring. In the United States, in Canada, and more recently in Ireland, where it was used as underfloor infill, pyrite contamination has caused major structural damage.
Concrete Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wid ...
exposed to sulfate ions, or sulfuric acid, degrades by
sulfate attack Cement hydration and strength development mainly depend on two silicate phases: tricalcium silicate (C3S) (alite), and dicalcium silicate (C2S) (belite). Upon hydration, the main reaction products are calcium silicate hydrates (C-S-H) and calcium ...
: the formation of expansive mineral phases, such as
ettringite Ettringite is a hydrous calcium aluminium sulfate mineral with formula: . It is a colorless to yellow mineral crystallizing in the trigonal system. The prismatic crystals are typically colorless, turning white on partial dehydration. It is part of ...
(small needle crystals exerting a huge crystallization pressure inside the concrete pores) and
gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywa ...
creates inner
tensile force In physics, tension is described as the pulling force transmitted axially by the means of a string, a rope, chain, or similar object, or by each end of a rod, truss member, or similar three-dimensional object; tension might also be described as t ...
s in the concrete matrix which destroy the hardened
cement A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel (aggregate) together. Cement mixe ...
paste, form cracks and fissures in concrete, and can lead to the ultimate ruin of the structure. Normalized tests for
construction aggregate Construction aggregate, or simply aggregate, is a broad category of coarse- to medium-grained particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates. Aggregate ...
certify such materials as free of pyrite or marcasite.


Occurrence

Pyrite is the most common of sulfide minerals and is widespread in igneous, metamorphic, and sedimentary rocks. It is a common accessory mineral in igneous rocks, where it also occasionally occurs as larger masses arising from an
immiscible Miscibility () is the property of two substances to mix in all proportions (that is, to fully dissolve in each other at any concentration), forming a homogeneous mixture (a solution). The term is most often applied to liquids but also appli ...
sulfide phase in the original magma. It is found in metamorphic rocks as a product of
contact metamorphism Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of che ...
. It also forms as a high-temperature hydrothermal mineral, though it occasionally forms at lower temperatures. Pyrite occurs both as a primary mineral, present in the original sediments, and as a secondary mineral, deposited during
diagenesis Diagenesis () is the process that describes physical and chemical changes in sediments first caused by water-rock interactions, microbial activity, and compaction after their deposition. Increased pressure and temperature only start to play a ...
. Pyrite and
marcasite The mineral marcasite, sometimes called “white iron pyrite”, is iron sulfide (FeS2) with orthorhombic crystal structure. It is physically and crystallographically distinct from pyrite, which is iron sulfide with cubic crystal structure. Both ...
commonly occur as replacement
pseudomorph In mineralogy, a pseudomorph is a mineral or mineral compound that appears in an atypical form ( crystal system), resulting from a substitution process in which the appearance and dimensions remain constant, but the original mineral is replaced ...
s after
fossils A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
in
black shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especiall ...
and other
sedimentary rocks Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particle ...
formed under reducing environmental conditions. Pyrite is common as an accessory mineral in shale, where it is formed by precipitation from anoxic seawater, and coal beds often contain significant pyrite. Notable deposits are found as lenticular masses in Virginia, U.S., and in smaller quantities in many other locations. Large deposits are mined at Rio Tinto in Spain and elsewhere in the Iberian Peninsula.


Cultural beliefs

In the beliefs of the Thai people (especially the southerner), pyrite is known by multiple names: ''Khao tok
Phra Ruang Phra Ruang ( th, พระร่วง) is a legendary figure from Thai history, usually described as the founder of the first Thai kingdom who freed the people from the rule of the ancient Khmer Empire. It is also found as a title that may ha ...
'', ''Khao khon bat Phra Ruang'' (ข้าวตอกพระร่วง, ข้าวก้นบาตรพระร่วง) or ''Phet na tang'', ''Hin na tang'' (เพชรหน้าทั่ง, หินหน้าทั่ง). It is believed to be a sacred item that has the power to prevent evil,
black magic Black magic, also known as dark magic, has traditionally referred to the use of supernatural powers or magic for evil and selfish purposes, specifically the seven magical arts prohibited by canon law, as expounded by Johannes Hartlieb in 14 ...
or demons.


Images

File:Bullypyrite2.jpg, As a replacement mineral in an
ammonite Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefis ...
from France File:Pyrite from Ampliación a Victoria Mine, Navajún, La Rioja, Spain 2.jpg, Pyrite from Ampliación a Victoria Mine, Navajún, La Rioja, Spain File:Pyrite-Tetrahedrite-Quartz-184642.jpg, Pyrite from the Sweet Home Mine, with golden striated cubes intergrown with minor tetrahedrite, on a bed of transparent quartz needles File:Pyrite-200582.jpg, Radiating form of pyrite File:Paraspirifer bownockeri.fond.jpg, '' Paraspirifer bownockeri'' in pyrite File:Fluorite-Pyrite-tmu38b.jpg, Pink fluorite perched between pyrite on one side and metallic galena on the other side File:Pyrite in pyrrhotite SEM image.png, SEM image of intergrowth of pyrite cuboctahedral crystals (yellow) and pyrrhotite (pinkish yellow)


See also

*
Iron–sulfur world hypothesis The iron–sulfur world hypothesis is a set of proposals for the origin of life and the early evolution of life advanced in a series of articles between 1988 and 1992 by Günter Wächtershäuser, a Munich patent lawyer with a degree in chemistry, ...
*
Sulfur isotope biogeochemistry Sulfur isotope biogeochemistry is the study of the distribution of sulfur isotopes in biological and geological materials. In addition to its common isotope, 32S, sulfur has three rare stable isotopes: 34S, 36S, and 33S. The distribution of these i ...


References


Further reading

* American Geological Institute, 2003, ''Dictionary of Mining, Mineral, and Related Terms'', 2nd ed., Springer, New York, . * David Rickard, ''Pyrite: A Natural History of Fool's Gold'', Oxford, New York, 2015, .


External links


Educational article about the famous pyrite crystals from the Navajun Mine


"Pyrite oxidation under room conditions". * {{Authority control Disulfides Firelighting Pyrite group Iron(II) minerals Cubic minerals Minerals in space group 205 Sulfide minerals Alchemical substances Semiconductor materials Transition metal dichalcogenides