Pyrite

• Iron pyrites
• Fool's gold, fool's gold
• Pyrite

Pyrite, also known as iron pyrites, fool's gold or fool's gold, is a very common mineral from the mineral class of " sulfides and sulfosalts ". Chemically, it is the cubic modification of the iron ( II) - disulfide with the chemical composition FeS2, that consists of iron and sulfur in the ratio of 1 to 2

Pyrite in any form is opaque (opaque ) and developed predominantly euhedral crystals in the form of cubes or pentagonal dodecahedron tetrahedra. Also octahedron and Disdodekaeder are common as well as combinations of these forms. The crystal faces show by twinning often a characteristic striation and a lively metallic luster in fresh condition.

With a Mohs hardness of 6 to 6.5 Pyrite is one of the hard minerals that are similar as the reference mineral orthoclase (6 ) can barely scratched with a steel file.

Special Features

Due to its metallic luster and its golden color was and is often confused with pyrite gold. Unlike genuine gold is not moldable, however, pyrite and substantially harder than the noble metal. In addition, pyrite leaves on the dash panel a distinct black line ( with an occasional tinge of greenish or bluish ), gold on the other hand a gold colored.

However, pyrite at some sites actually contain tiny amounts of gold, which can make it an economically recoverable ore.

Pyrite is soluble in nitric acid, concentrated hydrochloric acid and in hot concentrated sulfuric acid. When heated to about 743 ° C, the mineral decomposes. Above a temperature of 570 ° C to pyrite converts to pyrrhotite.

Pyrite is a natural semiconductor whose energy gap between the valence band and conduction band is reduced by the incorporation of foreign atoms. Doping with arsenic results in a p-type semiconductor. The band gap is between 0.8 and 1.8 eV. Whether this is due to direct or indirect band edge transitions, is still unclear. Usually an energy of 0.95 eV is indicated for the indirect transition.

Because of their semi-conductive property of natural pyrite pieces were formerly used in detector receivers as a crystal detector for demodulation. By contacting by hand according to the principle of a peak diode was sought with a needle suitable as a diode region on the stone.

The dielectric constant of pyrite is 20.8.

Etymology and history

The name Pyrite comes from the Greek pyr πυρ for fire. With a hard flint can refuse pyrite splinters that could ignite and burn:

This property has been used in the stone age to start fires.

Its tempting but deceptive golden luster brought the pyrite a popular name fool's gold, which is derived from the word " heretic ". In the English -speaking world it is called fool's gold, so " fools gold". Pyrite is also known in German as fools gold, but far less frequently. Perhaps the term was taken from English.

Pyrite and marcasite were long thought to be the same mineral; both were often referred to in the literature as pyrite or iron pyrite, marcasite parallel as. Mid-19th century it was recognized that the pyrite actually consisted of two different, albeit very similar minerals. Since then, pyrite and marcasite are run as independent minerals.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz pyrite belonged to the mineral class of " sulfides and sulfosalts " and then to the Department of " sulfides with the molar ratio of metal: sulfur, selenium, tellurium <1: 1 " where he named the " pyrite - group " with the system no. II/D.17 and the other members Aurostibit, Cattierit, Changchengit, Dzharkenit, Erlichmanit, Fukuchilit, Geversit, Hauerite, Insizwait, Krut'ait, Laurit, Maslovit, Mayingit, Michenerit, Padmait, Penroseite, Sperrylite, Testibiopalladit, Trogtalit, Vaesit and Villamaninit is.

The 9th edition valid since 2001 and of the International Mineralogical Association (IMA ) used the Strunz'schen Mineral classification assigns the pyrite also in the class of " sulfides and sulfosalts " (but expanded to include the selenides, tellurides, arsenides, antimonides, bismuthides, Sulfarsenite, Sulfantimonite, Sulfbismuthite ) and there in the department of " metal sulfides with the molar ratio M: S ≤ 1: 2". However, this is further subdivided by the exact molar ratio and the dominant in the compound metal ions, so that the mineral according to its composition in the subsection "M: S = 1: 2, with Fe, Co, Ni, PGE, etc. " is to be found where it also namesake of the still existing " pyrite Ggruppe " with the system no. Is 2.EB.05 and the other members Aurostibit, Bambollait, beta Iridisit, Cattierit, Dzharkenit, Erlichmanit, Fukuchilit, Gaotaiit, Geversit, Hauerite, Insizwait, Krut'ait, Laurit, Penroseite, Sperrylite, Trogtalit, Vaesit and Villamanínit.

The mainly common in English-speaking classification of minerals according to Dana assigns the pyrite in the class of " sulfides and sulfosalts " and then in the Department of " sulfide minerals ." Again, it forms the eponymous " pyrite group ( Isometric: Pa3 ) " with the system no. 02:12:01 and the other members Aurostibit, Cattierit, Dzharkenit, Erlichmanit, Fukuchilit, Gaotaiit, Geversit, Hauerite, Insizwait, Krut'ait, Krutovit, Laurit, Mayingit, Penroseite, Sperrylite, Trogtalit, Vaesit and Villamanínit within the subdivision " sulfides - selenides and tellurides, including - the composition AmBnXp, with ( n m ): P = 1: 2 ".

Modifications and varieties

The connection FeS2 is dimorphic, which means it comes in addition to the cubic pyrite crystallizing before crystallizing as orthorhombic marcasite.

Bravoit is a nickel-containing variety of pyrite.

Education and Locations

Pyrite is by far the most common sulphide minerals; he is part of most sulphide deposits and mafic rocks Beimineral the most. Also in hydrothermal veins, where it can be caused by crystallization eisensulfidhaltiger solutions, it finds itself. The soft parts of animals are often replaced in stagnant oxygen-free muddy environments by pyrite, so that pyrite also occurs in sedimentary rocks. Sulfur-reducing bacteria are here responsible for the deposition of very small crystals, which then convert to rock in compression of the deposits. At higher compression pyrite can grow into larger crystals and even replace shells or bones. In this way, fossils can be completely transformed. An example of this are those referred to as gold screw Ammonites of the Jurassic of the Franconian Alb. Under the influence of oxygen on the surface weathered pyrite via several intermediates to iron oxide ( limonite or brown iron ore ).

Finally, pyrite also occurs in lignite and hard coal as well as in oxygen-free groundwater aquifers. It is in this environment usually poorly crystallized and very sensitive to oxidation.

Worldwide, pyrite so far (as of 2011) are detected on nearly 30,000 localities, many of occurrence partially contain large pyrite masses ( " gravel body "). The largest pyrite cubes with an edge length of up to 30 cm were found in Climax in the U.S. state of Colorado. Well -crystallized pyrite with up to 20 cm in diameter appeared, among others, in Rio Marina on the island of Elba in Italy and in the " Samo Mine" at Hnúšťa in Slovakia, and to about 15 cm large crystals occurred in Huallanca (Huánuco ) and Santiago de Chuco evident in Peru.

Celebrity have also designated as the " Iron Cross " Crystal twins, two intergrown pyrite according to the law pentagonal dodecahedron, from the Weser mountain country around Vlotho and Extertal in Germany. Also known Nanisivik in Canada with his discoveries of complex crystal combinations.

With one of the largest deposits include Minas de Riotinto where the pyrite is in the form of fine-grained sediment with an estimated mass of about one billion tons, and also located in Spain Location Navajún (La Rioja ), where the largest cube shape found about 8 cm tall had.

Until 1992, one of the most important large-scale activity exploited deposits in Germany was Meggen in Sauerland (North Rhine -Westphalia). More Fund geographies covered include the Black Forest in Baden- Württemberg, Fichtelgebirge and Spessart in Bavaria, Brandenburg, Dillkreis and Odenwald in Hesse, the resin from Lower Saxony to Saxony -Anhalt, Mecklenburg- Vorpommern, the Eifel district of North Rhine -Westphalia to Rhineland -Palatinate, Saarland, the Ore Mountains Saxony, Schleswig -Holstein and Thuringia.

In Austria pyrite was detected at various locations in all provinces. In Switzerland, the mineral occurred mainly in the cantons of Aargau, Bern, Graubünden, Ticino, Uri, Valais and Vaud.

Even in rock samples of the Mid-Atlantic Ridge, the Central Indian Ridge, the East Pacific Rise, from Chinese, Japanese and Okhotsk Sea and beyond the Earth to the Moon ( Luna 20) was found pyrite.

Morphology

Pyrite occurs commonly in coarse, granular masses before or forms ball to raspberry-shaped, concentric -shell aggregates. Disc -shaped radiating aggregates ( pyrite sun) form sedimentary.

Well -formed crystals are common and can be great about 25 cm. About 60 forms are known. The most common forms are the cube { 100}, the pentagonal dodecahedron { 210 } and {111 } octahedron and combinations thereof. The pentagonal dodecahedron is found predominantly in pyrite crystals and therefore this form is also called Pyritoeder. A rare and usually only in combination with other forms we find the rhombic dodecahedron { 110}, { 221 } and trapezohedron the diploid { 321 }. Very rarely are curved strip-shaped crystals.

Dice, platy distorted

Pentagonal dodecahedron ( Pyritoeder ) { 210 }

Octahedron {111 }

Cuboctahedrons combination of {100 } and { 111}

Combination of { 210 } and { 111}

Combination of { 210 } and { 100}

Combination of {111 }, { 100} and { 110}

Strip-shaped pyrite

Brachiopod, replaced by pyrite

Pyrite ball

Tuber - spherical pyrite - limonite concretion (trade name Bojistein )

Pyritsonne

Crystal structure

Pyrite crystallizes in the cubic crystal class disdodekaedrischen in the space group Pa3 ( Raumgruppen-Nr. 205 ) with the lattice parameters a = 5.42 Å ( 542 pm ) and four formula units per unit cell.

Structurally, the pyrite is very similar to halite (also sodium chloride, NaCl), although the positively charged sodium ions replaced by iron ions and the singly negatively charged chlorine ions by dumbbell-shaped S2 groups, a disulfide ion, which is structurally equivalent to the peroxide ion, are. The bar axes are oriented parallel to the 3 -fold axis of rotation, but in a different orientation, which results in a lowering of the symmetry. Within the " sulfur dumbbell " prevails atomic bond between sulfur and iron ion binding, however.

Use

Commodity

Economically pyrite for the production of sulfuric acid, and occasionally for iron production. The remaining sulfuric acid in the extraction residue, the so-called Purpurerz (Fe2O3 ) or pyrite cinder is processed in blast furnaces for iron. In addition, pyrite is also known as polish and color raw material use.

When copper levels above 0.5 % copper is also recovered. The gold recovery, however, is only worthwhile for local enrichment.

In 1999, only about three million tons of pyrite were roasted for sulfuric acid production in Europe, the larger proportion of sulfuric acid is now obtained from the desulfurization of fossil fuels and other gases.

Gem

Although pyrite belongs to the group of mourning jewelry, but was also carried on other occasions and mostly processed into semi-precious stones in natural form as a pendant or brooch, but also honed including as stone ring or necklace. However, pyrite is not particularly useful since it is sensitive to heat, which is already prepared while grasping problems than wearing jewelry. Due to its sensitivity to acids " blind " the crystal surfaces with time. Since pyrite is very similar to marcasite, he often comes under this false name in the trade. Marcasite is, however, more sensitive and decomposes after a few years.

Importance for the environment

The pyrite contained in lignite and coal and other sulfur compounds enter the combustion process the sulfur present as sulfur dioxide ( SO2) in the flue gases from. When this gas reaches the atmosphere, forming in water droplets sulfurous acid, which significantly to the emergence of " acid rain " contributes. Measures of flue gas desulfurization, the sulfur dioxide can be today largely retained.

Also the pyrite contained in aquifers can be oxidized in the presence of oxygen. This oxidation is mainly catalyzed by bacteria. Has a great importance, the oxidation of pyrite by denitrifying, iron - sulfur-oxidizing bacteria and nitrate as the indirect oxidant. This is an existing of a plurality of abiotic and bacterial redox process in which the end of the sulfide sulfur contained in the pyrite is oxidized to sulfate ( SO42 - ) and nitrate to elemental, molecular nitrogen (N2) is reduced. We call this process as " denitrification " by pyrite. In the water catchment areas of the Stadtwerke Hannover AG annual order of 1,000 tons of pyrite be implemented in this way.

Since, according to the Drinking Water Ordinance, the limit for nitrate of 50 mg / l is lower than that of sulfate with 240 mg / l, mean denitrification by pyrite with regard to compliance with the nitrate limit a discharge. The iron contained in pyrite and other metallic accompanying elements such as manganese or nickel may partially occur in the water and must be eliminated in drinking water treatment.

The pyrite contained in the lignite is one of the requirements for the acidification of residual holes eg in Lusatia by acid heap waters.

Esoteric

From esoteric pyrite is used as a healing stone for arthritis and sciatica. Radialstrahlig grown pyrite - a so-called " pyrite sun " - is worn as an amulet pendant around the neck for an act against stomach and digestive disorders and on the other to strengthen the immune system. Scientific evidence for the effectiveness, however, are not available.