The
mineralA mineral is a naturally occurring solid formed through geological processes that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties. A rock, by comparison, is an aggregate of minerals and/or mineraloids, and need not have a specific...
pyrite, or
iron pyrite, is an iron
sulfideA sulfide is a chemical compound containing sulfur in its lowest oxidation number of −2.- Properties :...
with the
formulaA chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
FeIron is a metallic chemical element with the symbol Fe and atomic number 26. Iron is a group 8 and period 4 element and is therefore classified as a transition metal. Iron and iron alloys are by far the most common metals and the most common ferromagnetic materials in everyday use...
SSulfur or sulphur is the chemical element that has the atomic number 16. It is denoted with the symbol S. It is an abundant, multivalent non-metal. Sulfur, in its native form, is a yellow crystalline solid. In nature, it can be found as the pure element and as sulfide and sulfate minerals...
2. This mineral's metallic
lusterLustre is a description of the way light interacts with the surface of a crystal, rock, or mineral. For example, a diamond is said to have an adamantine lustre and pyrite is said to have a metallic lustre...
and pale-to-normal, brass-yellow hue have earned it the nickname
fool's gold due to its resemblance to
goldGold is a chemical element with the symbol Au and an atomic number of 79. It has been a highly sought-after precious metal for coinage, jewelry, and other arts since the beginning of recorded history. The metal occurs as nuggets or grains in rocks, in veins and in alluvial deposits. Gold is...
. The color has also led to the nicknames
brass,
brazzle and
brazil, primarily used to refer to pyrite found in
coalCoal is a readily combustible black or brownish-black sedimentary rock normally occurring in rock strata in layers or veins called coal beds. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...
.
Pyrite is the most common of the
sulfide mineralA sulfide mineral is a mineral containing sulfide as the major anion. Sulfides 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.Common or important...
s. The name pyrite is derived from the
GreekGreek , an independent branch of the Indo-European family of languages, is the language of the Greeks. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. In its ancient form, it is the language of classical...
πυρίτης (puritēs), “of fire” or "in fire”, from
πύρ (pur), “fire”. This name is likely due to the sparks that result when pyrite is struck against
steelSteel is an alloy consisting mostly of iron, with a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most cost-effective alloying material for iron, but various other alloying elements are used such as manganese, chromium, vanadium, and tungsten...
or
flintFlint is a hard, sedimentary cryptocrystalline form of the mineral quartz, categorized as a variety of chert. It occurs chiefly as nodules and masses in sedimentary rocks, such as chalks and limestones. Inside the nodule, flint is usually dark grey, black, green, white, or brown in color, and...
. This property made pyrite popular for use in early
firearmA firearm is a device which projects either single or multiple projectiles at high velocity through a controlled explosion. The firing is achieved by the gases produced through rapid, confined burning of a propellant. This process of rapid burning is technically known as deflagration...
s such as the
wheellockWheellock, wheel-lock or wheel lock, is a mechanism for firing a firearm. It was the next major development in firearms technology after the matchlock and the first self-igniting firearm. The mechanism is so-called because it uses a rotating steel wheel to provide ignition...
.
Pyrite is usually found associated with other sulfides or
oxideAn oxide is a chemical compound containing at least one oxygen atom as well as at least one other element. Most of the Earth's crust consists of oxides. Oxides result when elements are oxidized by oxygen in air. Combustion of hydrocarbons affords the two principal oxides of carbon, carbon...
s in
quartzQuartz is the second most abundant mineral in the Earth's continental crust . It is made up of a continuous framework of SiO
4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO
2.There are many different varieties of...
veinsIn geology, a vein is a finite volume within a rock, having a distinct shape, filled with crystals of one or more minerals, which were precipitated from an fluid....
,
sedimentary rockSedimentary rock is the type of rock that is formed by sedimentation of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....
, and
metamorphic rockMetamorphic rock is the result of the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure causing profound physical and/or chemical change...
, as well as in
coalCoal is a readily combustible black or brownish-black sedimentary rock normally occurring in rock strata in layers or veins called coal beds. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...
beds, and as a replacement mineral in
fossilFossils are the preserved remains or traces of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous rock formations and sedimentary layers is known as the fossil record...
s. Despite being nicknamed fool's gold, small quantities of
goldGold is a chemical element with the symbol Au and an atomic number of 79. It has been a highly sought-after precious metal for coinage, jewelry, and other arts since the beginning of recorded history. The metal occurs as nuggets or grains in rocks, in veins and in alluvial deposits. Gold is...
are sometimes found associated with pyrite. Gold and arsenic occur as a coupled substitution in the pyrite structure. In the
Carlin, NevadaCarlin is a town located near the western border of Elko County in northeast Nevada, west of the city of Elko. It is part of the Elko Micropolitan Statistical Area. Carlin sits along Interstate 80 at an elevation of approximately . As of the 2000 census, its population was 2,161...
gold deposit, arsenian pyrite contains up to 0.37 wt% gold. Auriferous pyrite is a valuable
oreAn ore is a type of rock that contains minerals such as gemstones or 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...
of gold.
Weathering and release of sulfate
Pyrite exposed to the atmosphere during
miningMining is the extraction of valuable minerals or other geological materials from the earth, usually from an ore body, vein or seam. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock salt and potash...
and excavation reacts with
oxygenOxygen Oxygen Oxygen (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O...
and
waterWater is an ubiquitous chemical substance that is composed of hydrogen and oxygen and is essential for all known forms of life.In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71%...
to form
sulfateIn inorganic chemistry, a sulfate is a salt of sulfuric acid.-Chemical properties:...
, resulting in
acid mine drainageAcid mine drainage , or acid rock drainage , refers to the outflow of acidic water from metal mines or coal mines. However, other areas where the earth has been disturbed may also contribute acid rock drainage to the environment...
. This acidity results from the action of
AcidithiobacillusAcidithiobacillus is a genus of proteobacteria. The members of this genus used to belong to Thiobacillus, before they were reclassified in the year 2000....
bacteria, which generate their energy by oxidizing ferrous iron (Fe
2+) to ferric iron (Fe
3+) using
oxygenOxygen Oxygen Oxygen (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O...
. The ferric iron in turn attacks the pyrite to produce ferrous iron and sulfate. The ferrous iron is then available for oxidation by the bacterium; this cycle continues until the pyrite is depleted.
Uses
Pyrite is used commercially for the production of
sulfur dioxideSulfur dioxide is the chemical compound with the formula SO
2. It is produced by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide...
, for use in such applications as the paper industry, and in the manufacture of sulfuric acid.
During the early years of the 20th century, pyrite was used as a mineral detector in
radioRadio is the transmission of signals by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
receivers, and is still used by 'crystal radio' hobbyists. Until the
vacuum tubeIn electronics, a vacuum tube, electron tube , thermionic valve, or valve is a device used to amplify, switch, otherwise modify, or create an electrical signal by controlling the movement of electrons in a low-pressure space...
matured, the crystal detector was the most sensitive and dependable detector available- with considerable variation between mineral types and even individual samples within a particular type of mineral. The most sensitive mineral was
galenaGalena is the natural mineral form of lead sulfide. It is the most important lead ore mineral.Galena is one of the most abundant and widely distributed sulfide minerals. It crystallizes in the cubic crystal system often showing octahedral forms...
, which was very sensitive also to mechanical vibration, and easily knocked off the sensitive point; the most stable were perikon mineral pairs; and midway between was the pyrites detector, which is approximately as sensitive as a modern 1N34A
diodeIn electronics a diode is a two-terminal electronic component which conducts electric current asymmetrically or unidirectionally; that is, it conducts current more easily in one direction than in the opposite direction. The term usually refers to a semiconductor diode, the most common type today,...
detector.
Pyrite has been proposed as an abundant inexpensive material in low cost photovoltaic solar panels.
Formal oxidation states for pyrite, marcasite, and arsenopyrite
From the perspective of classical inorganic chemistry, which assigns formal oxidation states to each atom, pyrite is probably best described as Fe
2+S
22-. This formalism recognizes that the sulfur atoms in pyrite occur in pairs with clear S-S bonds. These persulfide units can be viewed as derived from hydrogen persulfide,
HHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H
2...
2S
2. Thus pyrite would be more descriptively called iron persulfide, not iron disulfide. In contrast,
molybdeniteMolybdenite is a mineral of molybdenum disulfide, MoS
2. 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 atoms sandwiched between sheets...
,
MoMolybdenum , is a Group 6 chemical element with the symbol Mo and atomic number 42. The free element, which is a silvery metal, has the sixth-highest melting point of any element. It readily forms hard, stable carbides, and for this reason it is often used in high-strength steel alloys...
S
2, features isolated sulfide (S
2-) centers. Consequently, the oxidation state of molybdenum is Mo
4+. The mineral arsenopyrite has the formula Fe
AsArsenic is the chemical element that has the symbol As, atomic number 33 and atomic mass 74.92. Arsenic was first documented by Albertus Magnus in 1250. Arsenic is a notoriously poisonous metalloid with many allotropic forms, including a yellow and several black and grey forms...
S. Whereas pyrite has S
2 subunits, arsenopyrite has AsS units, formally derived from
deprotonationDeprotonation is a chemistry term that refers to the removal of a proton from a molecule, forming the conjugate base. The relative ability for a molecule to give up a proton is measured by a pKa value. A low pKa value indicates that the compound is acidic and will easily...
of H
2AsSH. Analysis of classical oxidation states would recommend the description of arsenopyrite as Fe
3+AsS
3-.
Crystallography
Iron-pyrite FeS
2 represents the prototype compound of the crystallographic pyrite structure. The structure is simple
cubicThe cubic crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals....
and was among the first crystal structures solved by x-ray diffraction . It belongs to the crystallographic
space groupIn crystallography, the space group of a crystal is a description of the symmetry of the crystal, and can have one of 230 types...
Pa and is denoted by the Strukturbericht notation C2. Under thermodynamic standard conditions the
lattice constantThe Lattice Constant [or lattice parameter] refers to the constant distance between unit cells in a crystal lattice. Lattices in three dimensions generally have three lattice constants, referred to as a, b, and c. However, in the special case of cubic crystal structures, all of the constants are...
of stoichiometric iron pyrite FeS
2 amounts to 541.87 pm . The unit cell is composed of a Fe
face-centered cubic sublatticeIn geometry and crystallography, a Bravais lattice, studied by , is an infinite set of points generated by a set of discrete translation operations described by:...
into which the S ions are embedded. The pyrite structure is also taken by other compounds
MX2 of transition metals
M and
chalcogensThe chalcogens are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family...
X =
OOxygen Oxygen Oxygen (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O...
,
SSulfur or sulphur is the chemical element that has the atomic number 16. It is denoted with the symbol S. It is an abundant, multivalent non-metal. Sulfur, in its native form, is a yellow crystalline solid. In nature, it can be found as the pure element and as sulfide and sulfate minerals...
,
SeSelenium is a chemical element with the atomic number 34, represented by the chemical symbol Se, an atomic mass of 78.96. It is a nonmetal, chemically related to sulfur and tellurium, and rarely occurs in its elemental state in nature....
and
TeTellurium is a chemical element that has the symbol Te and atomic number 52. A brittle silver-white metalloid which looks similar to tin, tellurium is chemically related to selenium and sulfur. Tellurium is primarily used in alloys and as a semiconductor.-Characteristics:Tellurium is extremely...
. Also certain dipnictides with
X standing for
PPhosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus is commonly found in inorganic phosphate rocks. Elemental phosphorus exists in two major forms - white phosphorus and red phosphorus...
,
AsArsenic is the chemical element that has the symbol As, atomic number 33 and atomic mass 74.92. Arsenic was first documented by Albertus Magnus in 1250. Arsenic is a notoriously poisonous metalloid with many allotropic forms, including a yellow and several black and grey forms...
and
SbAntimony is a chemical element with the symbol Sb and atomic number 51. A metalloid, antimony has four allotropic forms. The stable form of antimony is a blue-white metalloid. Yellow and black antimony are unstable non-metals...
etc. are known to adopt the pyrite structure .
The positions of
X ions in the pyrite structure may be derived from the
fluoriteFluorite is a halide mineral composed of calcium fluoride, CaF
2. It is an isometric mineral with a cubic habit, though octahedral and more complex isometric forms are not uncommon. Cubic crystals up to 20 cm across have been found at Dalnegorsk, Russia...
structure: whereas
FFluorine is the chemical element with atomic number 9, represented by the symbol F. Fluorine forms a single bond with itself in elemental form, resulting in the diatomic F
2 molecule. F
2 is a supremely reactive, poisonous, pale, yellowish brown gas. Elemental fluorine is the...
ions in CaF
2 occupy the centre positions of the eight subcubes of the cubic unit cell (¼ ¼ ¼) etc., the S ions in FeS
2 are shifted from these high symmetry positions along <111> axes to reside on (
uuu) and symmetry-equivalent positions. Here, the parameter
u should be regarded as a free lattice parameter that takes different values in different pyrite-structure compounds (iron pyrite FeS
2:
u(S) = 0.385 ). In the first bonding sphere, Fe ions are surrounded by six S nearest neighbours, while S ions have bonds with three Fe and one S ion. The site symmetry at Fe and S positions is accounted for by
point symmetry groupsIn crystallography, a crystallographic point group is a set of symmetry operations, like rotations or reflections, that leave a point fixed while moving each atom of the crystal to the position of an atom of the same kind. That is, an infinite crystal would look exactly the same before and after...
C3i and
C3, respectively. The missing
center of inversionThe term centrosymmetric, as generally used in crystallography, refers to a space group which contains an inversion center as one of its symmetry elements. In such a space group, for every point in the unit cell there is an indistinguishable point...
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 sulphur 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 constantsThe 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....
and has to be included in the calculation of the
lattice energyThe lattice energy of an ionic solid is a measure of the strength of bonds in that ionic compound. It is usually defined as the enthalpy of formation of the ionic compound from gaseous ions and as such is invariably exothermic...
by using a generalised
Born-Haber cycleThe Born-Haber cycle is an approach to analyzing reaction energies. It was named after and developed by the two German scientists Max Born and Fritz Haber....
.
Varieties
Bravoite is a nickel-cobalt bearing variety of pyrite, with >50% substitution of
NiNickel is a chemical element, with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. It is one of the four ferromagnetic elements at about room temperature, other three being iron, cobalt and gadolinium...
2+ for Fe
2+ within pyrite. Bravoite is not a formally recognised mineral, and is named after Peruvian scientist Jose J. Bravo (1874-1928).
CattieriteCattierite is a mineral found in the Democratic Republic of Congo. It was discovered together with Vaesite by Johannes F. Vaes, a Belgian mineralologist and named after Felicien Cattier, Chairman of the Board, Union Miniere du Haut Katanga....
(
CoCobalt is a hard, lustrous, gray metal, a chemical element with symbol Co and atomic number 27. Although cobalt-based colors and pigments have been used since ancient times for making jewelry and paints, and miners have long used the name kobold ore for some minerals, the free metallic cobalt was...
SSulfur or sulphur is the chemical element that has the atomic number 16. It is denoted with the symbol S. It is an abundant, multivalent non-metal. Sulfur, in its native form, is a yellow crystalline solid. In nature, it can be found as the pure element and as sulfide and sulfate minerals...
2) and
VaesiteVaesite is a mineral found together with cattierite in the Democratic Republic of Congo. It is named after Johannes F. Vaes, a Belgian mineralologist.-References:**...
(
NiNickel is a chemical element, with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. It is one of the four ferromagnetic elements at about room temperature, other three being iron, cobalt and gadolinium...
SSulfur or sulphur is the chemical element that has the atomic number 16. It is denoted with the symbol S. It is an abundant, multivalent non-metal. Sulfur, in its native form, is a yellow crystalline solid. In nature, it can be found as the pure element and as sulfide and sulfate minerals...
2) are similar in their structure and belong also to the pyrite group.
Distinguishing similar minerals
ChalcopyriteChalcopyrite is a copper iron sulfide mineral that crystallizes in the tetragonal system. It has the chemical composition CuFeS
2....
is brighter yellow with a greenish hue when wet and is softer (3.5-4 on Mohs' scale).
ArsenopyriteArsenopyrite 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...
is silver white and does not become more yellow when wet.
External links