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Pyrite

A mass of intergrown pyrite crystals
General
Category Sulfide mineral
Chemical formula iron disulfide (FeS2)
Strunz classification II/D.17-30
Dana classification 2.12.1.1
Crystal symmetry 2/m3
Identification
Color Pale brass yellow, dull gold
Crystal habit Cubic, faces may be striated, but also frequently octahedral and pyritohedron. Often inter-grown, massive, radiated, granular, globular and stalactitic.
Crystal system Isometric Diploidal, Space group Pa-3
Twinning Penetration twinning
Cleavage Indistinct on {001}; partings on {011} and {111}
Fracture Very uneven, sometimes conchoidal
Mohs scale hardness 6–6.5
Luster Metallic, glistening
Streak Greenish-black to brownish-black; smells of sulfur
Specific gravity 4.95–5.10
Refractive index Opaque
Fusibility 2.5–3 to a magnetic globule
Solubility insoluble in water
Other characteristics paramagnetic
References [1][2][3][4]

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 due to its resemblance to gold. The color has also led to the nicknames brass, brazzle and brazil, primarily used to refer to pyrite found in coal.[5][6]

Pyrite is the most common of the sulfide minerals. The name pyrite is derived from the Greek πυρίτης (puritēs), “of fire” or "in fire”, from πύρ (pur), “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.[7] By Georgius Agricola's time, the term had become a generic term for all of the sulfide minerals.[8]

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. Despite being nicknamed fool's gold, small quantities of gold are sometimes found associated with pyrite. Gold and arsenic occur as a coupled substitution in the pyrite structure. In the Carlin, Nevada, gold deposit, arsenian pyrite contains up to 0.37 wt% gold.[9] Auriferous pyrite is a valuable ore of gold.

Contents

Weathering and release of sulfate

Pyrite exposed to the atmosphere during mining and excavation reacts with oxygen and water to form sulfate, resulting in acid mine drainage. This acidity results from the action of Acidithiobacillus bacteria, which generate their energy by oxidizing ferrous iron (Fe2+) to ferric iron (Fe3+) using oxygen. 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.

Iron pyrite oxidation is sufficiently exothermic that underground coal mines in high-sulfur coal seams have occasionally had serious problems with spontaneous combustion in the mined-out areas of the mine. The solution is to hermetically seal the mined-out areas to exclude oxygen.[10]

In modern coal mines, limestone dust is sprayed onto the exposed coal surfaces to reduce the hazard of dust explosions. 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 sulfates formed may exert crystallization pressure that can expand cracks in the rock and lead eventually to roof fall.[11]

Building stone containing pyrite tends to stain brown as the pyrite oxidizes. This problem appears to be significantly worse if any marcasite is also present.[12] The presence of pyrite in the aggregate used to make concrete can lead to severe deterioration as the pyrite oxidizes.[13] In early 2009, problems with Chinese drywall imported into the United States after Hurricane Katrina were attributed to oxidation of pyrite.[14]

Uses

Pyrite from Ampliación a Victoria Mine, Navajún, La Rioja, Spain

Pyrite enjoyed brief popularity in the 16th and 17th centuries as a source of ignition in early firearms, most notably the wheellock, where the cock held a lump of pyrite against a circular file to strike the sparks needed to fire the gun.

Pyrite has been used since classical times to manufacture copperas, or iron sulfate. Iron pyrite was heaped up and allowed to weather as described above (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, oil of vitriol (sulfuric acid) was manufactured either from copperas or by burning sulfur to sulfur dioxide and then converting that to sulfuric acid. By the 19th century, the dominant method was to burn iron pyrite.[15] Pyrite remains in commercial use for the production of 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 radio receivers, and is still used by 'crystal radio' hobbyists. Until the vacuum tube 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 galena, 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 diode detector.[16][17]

Pyrite has been proposed as an abundant inexpensive material in low cost photovoltaic solar panels.[18] Synthetic iron sulfide is used with copper sulfide to create the experimental photovoltaic material. [19]

Pyrite is used to make marcasite jewellery (incorrectly termed marcasite). Marcasite jewellery, made from small faceted pieces of pyrite, often set in silver, was popular in the Victorian era.[20]

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 Fe2+S22−. 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 disulfide, H2S2. Thus pyrite would be more descriptively called iron persulfide, not iron disulfide. In contrast, molybdenite, MoS2, features isolated sulfide (S2−) centers. Consequently, the oxidation state of molybdenum is Mo4+. The mineral arsenopyrite has the formula FeAsS. Whereas pyrite has S2 subunits, arsenopyrite has AsS units, formally derived from deprotonation of H2AsSH. Analysis of classical oxidation states would recommend the description of arsenopyrite as Fe3+AsS3−.[21]

Crystallography

Crystal structure of pyrite

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.[22] It belongs to the crystallographic space group Pa3 and is denoted by the Strukturbericht notation C2. Under thermodynamic standard conditions the lattice constant a of stoichiometric iron pyrite FeS2 amounts to 541.87 pm.[23] The unit cell is composed of a Fe face-centered cubic sublattice into which the S ions are embedded. The pyrite structure is also taken 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.[24]

The positions of X ions in the pyrite structure may be derived from the fluorite structure: whereas F ions in CaF2 occupy the centre positions of the eight subcubes of the cubic unit cell (¼ ¼ ¼) 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 lattice parameter that takes different values in different pyrite-structure compounds (iron pyrite FeS2: u(S) = 0.385 [25]). 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 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 sulphur lattice site, which causes a polarisation of S ions in the pyrite lattice.[26] 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.

Varieties

Bravoite 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 Peruvian scientist Jose J. Bravo (1874-1928).[27]

Cattierite (CoS2) and Vaesite (NiS2) are similar in their structure and belong also to the pyrite group.

Distinguishing similar minerals

Chalcopyrite is brighter yellow with a greenish hue when wet and is softer (3.5-4 on Mohs' scale).[28]

Arsenopyrite is silver white and does not become more yellow when wet.

Gallery

The following images show pyrite forms:

See also

References

  1. ^ Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., John Wiley and Sons, New York, p 285-286, ISBN 0-471-80580-7
  2. ^ http://webmineral.com/data/Pyrite.shtml Webmineral
  3. ^ http://www.mindat.org/min-3314.html Pyrite on Mindat.org
  4. ^ http://rruff.geo.arizona.edu/doclib/hom/pyrite.pdf Handbook of Mineralogy
  5. ^ Julia A. Jackson, James Mehl and Klaus Neuendorf, Glossary of Geology, American Geological Institute, 2005; page 82.
  6. ^ Albert H. Fay, A Glossary of the Mining and Mineral Industry, United States Bureau of Mines, 1920; pages 103-104.
  7. ^ James Dwight Dana, Edward Salisbury Dana, Descriptive Minerology, 6th Ed., Wiley, New York, 1911; page 86.
  8. ^ Herbert Clark Hoover and Lou Henry Hoover, translators of Georgius Agricola, [De Re Metallica], The Mining Magazine, London, 1912 (Dover reprint, 1950); see footnote, page 112.
  9. ^ http://www.minsocam.org/msa/AmMin/toc/Articles_Free/1997/Fleet_p182-193_97.pdf MICHAEL E. FLEETl AND A. HAMID MUMIN, Gold-bearing arsenian pyrite and marcasite and arsenopyrite from Carlin Trend gold deposits and laboratory synthesis, American Mineralogist, Volume 82, pages 182-193, 1997
  10. ^ Andrew Roy, Coal Mining in Iowa, Coal Trade Journal, quoted in History of Lucas County Iowa, State Historical Company, Des Moines, 1881; pages 613-615.
  11. ^ Erwin L. Zodrow, Colliery and surface hazards through coal-pyrite oxidation (Pennsylvanian Sydney Coalfield, Nova Scotia, Canada, International Journal of Coal Geology, Vol. 64, No. 1-2, Oct. 17, 2005; pages 145-155.
  12. ^ Oliver Bowles, The Structural and Ornamental Stones of Minnesota, Bulletin 663, United States Geological Survey, Washington, 1918; page 25.
  13. ^ Arezki Tagnit-Hamou, Mladenka Saric-Coric, Patrice Rivard, Internal deterioration of concrete by the oxidation of pyrrhotitic aggregates, Cement and Concrete Research, Vol. 35, No. 1, Jan. 2005; pages 99-107.
  14. ^ William Angelo, A Material Odor Mystery Over Foul-Smelling Drywall, from the web site of Engineering News Record Construction, dated 1/28/2009.
  15. ^ Industrial England in the Middle of the Eighteenth Century, Nature, Vol, 83, No. 2113, Thursday, April 28, 1910; pages 267-268.
  16. ^ The Principles Underlying Radio Communication, Radio Pamphlet No. 40, U.S. Army Signal Corps, Dec. 10, 1918; section 179, pages 302-305.
  17. ^ Thomas H. Lee, The Design of Radio Frequency Integrated Circuits, 2nd Ed., Cambridge University Press, 2004; pages 4-6.
  18. ^ Wadia, Kammen and Alivisatos, http://pubs.acs.org, Environmental Science & Technology. Environ. Sci. Technol., 2009, 43 (6), pp 2072–2077 DOI: 10.1021/es8019534 Publication Date (Web): February 13, 2009
  19. ^ Wadia, Kammen, Alivisatos article announcement http://www.berkeley.edu/news/media/releases/2009/02/17_solar.shtml
  20. ^ Hesse, Rayner W. (2007). Jewelrymaking Through History: An Encyclopedia. Greenwood Publishing Group. pp. 15. ISBN 0313335079. http://books.google.co.uk/books?id=IVgU0icm948C&pg=PA15. 
  21. ^ Vaughan, D. J.; Craig, J. R. “Mineral Chemistry of Metal Sulfides" Cambridge University Press, Cambridge: 1978. ISBN 0521214890
  22. ^ W. L. Bragg (1913). "The structure of some crystals as indicated by their diffraction of X-rays". Proc. Roy. Soc. Lond., Ser. A 89: 248–277. 
  23. ^ M. Birkholz, S. Fiechter, A. Hartmann, and H. Tributsch (1991). "Sulfur deficiency in iron pyrite (FeS2-x) and its consequences for band structure models". Phys. Rev. B 43: 11926. doi:10.1103/PhysRevB.43.11926. 
  24. ^ N. E. Brese, and H. G. von Schnering (1994). "Bonding Trends in Pyrites and a Reinvestigation of the Structure of PdAs2, PdSb2, PtSb2 and PtBi2". Z. anorg. allg. Chem. 620: 393. doi:10.1002/zaac.19946200302. 
  25. ^ E. D. Stevens, M. L. de Lucia, and P. Coppens (1980). "Experimental observation of the Effect of Crystal Field Splitting on the Electron Density Distribution of Iron Pyrite". Inorg. Chem. 19: 813. doi:10.1021/ic50206a006. 
  26. ^ M. Birkholz (1992). "The crystal energy of pyrite". J. Phys.: Condens. Matt. 4: 6227. doi:10.1088/0953-8984/4/29/007. 
  27. ^ http://www.mindat.org/min-759.html Mindat - bravoite
  28. ^ http://www.minerals.net/mineral/sulfides/pyrite/pyrite.htm Pyrite on Minerals.net
  • American Geological Institute, 2003, Dictionary of Mining, Mineral, and Related Terms, 2nd ed., Springer, New York, ISBN 978-3540012719
  • Mineral galleries

External links

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Simple English

Pyrite
File:Pyrite
A mass of intergrown pyrite crystals
General
CategorySulphide mineral
Chemical formulairon disulfide (FeS2)
Identification
ColorPale brass-yellow, tarnishes darker and iridescent
Crystal habitCubic
Crystal systemIsometric Diploidal, Space group Pa3
Mohs Scale hardness6–6.5
LusterMetallic, glistening
StreakGreenish-black to brownish-black; smells of sulphur
Specific gravity4.95–5.10
SolubilityInsoluble in water
Other Characteristicsparamagnetic

The mineral pyrite,[1] or iron pyrite, is an iron sulfide with the formula FeS2. This mineral's metallic lustre and pale-to-normal, brass-yellow colour have earned it the nickname fool's gold because of its resemblance to gold. [2][3][4][5][6][7] The term pyrite may also be used for some other sulphides such as copper sulphide.

History

Pyrite is the most common of the sulphide minerals. 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.[8] By Georgius Agricola's time, the term had become a generic term for all of the sulphide minerals.[9]

Pyrite is usually found associated with other sulphides or oxides in quartz veins, sedimentary rock, and metamorphic rock, as well as in coal beds, and as a replacement mineral in fossils. Despite being nicknamed fool's gold, pyrite is sometimes found in association with small quantities of gold.

References

  1. The name pyrite is derived from the Greek πυρίτης (puritēs), "of fire" or "in fire", from πύρ (pur), "fire".
  2. Julia A. Jackson, James Mehl and Klaus Neuendorf, Glossary of Geology, American Geological Institute (2005) p82.
  3. Albert H. Fay, A glossary of the mining and mineral industry, United States Bureau of Mines (1920) pp. 103–104.
  4. Hurlbut, Cornelius S.; Klein, Cornelis 1985. Manual of Mineralogy. 20th ed, John Wiley and Sons, New York. 285–286 ISBN 0-471-80580-7
  5. Pyrite on webmineral
  6. Pyrite on Mindat.org
  7. Handbook of Mineralogy
  8. James Dwight Dana, Edward Salisbury Dana, Descriptive Minerology, 6th ed., Wiley, New York (1911) p86.
  9. Herbert Clark Hoover and Lou Henry Hoover, translators of Georgius Agricola, [De Re Metallica], The Mining Magazine, London (1912; Dover reprint, 1950); see footnote, p112.


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