page_title: Pyrite
section_title: Crystallography
hierarchical_section_title: Pyrite / Crystallography
caption_attribution_description: English: Iron sulfide-type structure. Same for ZnO2. Yellow atoms are sulfur (or oxygen) Journal = JOURNAL OF ALLOYS AND COMPOUNDS Year = 1992 Volume = 178 Page = 181-191 Title = Preparation and electrical transport properties of pyrite (FeS2) single crystals Authors = Willeke G., Blenk O., Kloc C., Bucher E.
context_page_description: The mineral pyrite, or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula FeS₂. Pyrite is the most abundant sulfide mineral.
  Pyrite's metallic luster and pale brass-yellow hue give it a superficial resemblance to gold, 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.
  The name pyrite is derived from the Greek πυρίτης λίθος, "stone or mineral which strikes fire", in turn from πῦρ, "fire". In ancient Roman times, this name was applied to several types of stone that would create sparks when struck against steel; Pliny the Elder described one of them as being brassy, almost certainly a reference to what we now call pyrite.
  By Georgius Agricola's time, c. 1550, the term had become a generic term for all of the sulfide minerals.
  Pyrite is usually found associated with other sulfides or oxides in quartz veins, sedimentary rock, and metamorphic rock, as well as in coal beds and as a replacement mineral in fossils, but has also been identified in the sclerites of scaly-foot gastropods.
context_section_description: Iron-pyrite FeS₂ represents the prototype compound of the crystallographic pyrite structure. The structure is simple cubic and was among the first crystal structures solved by X-ray diffraction. It belongs to the crystallographic space group Pa3 and is denoted by the Strukturbericht notation C2. Under thermodynamic standard conditions the lattice constant  of stoichiometric iron pyrite FeS₂ amounts to 541.87 pm. The unit cell is composed of a Fe face-centered cubic sublattice into which the S
  ₂ ions are embedded. (Note though that the structure is simple cubic with four iron atoms per cubic unit cell, not face-centered cubic. The iron atoms in the faces are not equivalent by translation alone to the iron atoms at the corners.) The pyrite structure is also used by other compounds MX₂ of transition metals M and chalcogens X = O, S, Se and Te. Also certain dipnictides with X standing for P, As and Sb etc. are known to adopt the pyrite structure.
  In the first bonding sphere, the Fe atoms are surrounded by six S nearest neighbours, towards six of the eight faces of a distorted octahedron. The material is a semiconductor and the Fe ions should be considered to be in a low spin divalent state (as shown by Mössbauer spectroscopy as well as XPS), rather than a tetravalent state as the stoichiometry would suggest. The material as a whole acts as a Van Vleck paramagnet, despite its low-spin divalency. 
  The positions of X ions in the pyrite structure may be derived from the fluorite structure, starting from a hypothetical Fe²⁺(S⁻)₂ structure. Whereas F⁻ ions in CaF₂ occupy the centre positions of the eight subcubes of the cubic unit cell (​¹⁄₄ ​¹⁄₄ ​¹⁄₄) etc., the S⁻ ions in FeS₂ 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 atomic parameter that takes different values in different pyrite-structure compounds (iron pyrite FeS₂: u(S) = 0.385). The shift from fluorite u = 0.25 to pyrite u = 0.385 is rather large and creates an S–S distance that is clearly a binding one. This is not surprising as in contrast to F⁻ an ion S⁻ is not a closed shell species. It is isoelectronic with a chlorine atom, also undergoing pairing to form Cl₂ molecules. Both low spin Fe²⁺ and the disulfide S₂²⁻ moeties are closed shell entities, explaining the diamagnetic and semiconducting properties.
  The S atoms have bonds with three Fe and one other S atom. The site symmetry at Fe and S positions is accounted for by point symmetry groups C₃ᵢ and C₃, 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 constants and has to be included in the calculation of the lattice energy by using a generalised Born–Haber cycle. 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 homoatomic ones. Marcasite also possesses homoatomic anion pairs, but the arrangement of the metal and diatomic anions is different from that of pyrite. Despite its name a chalcopyrite (CuFeS
  ₂) does not contain dianion pairs, but single S²⁻ sulfide anions.
caption: Crystal structure of pyrite. In the center of the cell a S22− pair is seen in yellow
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