Pyrite
Pyrite is everywhere, it is a very common but also very collectible mineral, that has
been known to man since Antiquity. One of the earliest mentions is by Theophrastus
(app. 372 BC-app. 287 BC) who in his work 'On Stones' mentions grains of Pyrite
imbedded in Lapis Lazuli.
Geology
Pyrite is a so-called persistent mineral, forming under virtually all conditions of mineral
formation. It is very frequent in sediments, as either fine grains or replacing fossils, and
metamorphosed sediments (f.ex. Minas Victoria, Navajun, Logrono, La Rioja, Spain)
may carry spectacular, crystallised Pyrite. It is very common in hydrothermal and
mesothermal veins, accompanying other ore minerals, and one of the worlds largest
Pyrite deposits (Rio Tinto, Spain) is a medium to high-temperature hydrothermal
deposit. It is infrequent but does occur in igneous rocks like granites and pegmatites.
Pyrite is easily oxidised, forming iron sulfates and ultimately Limonite. The 'eisener
Hut' (German) or gossan (English) of ore deposits is an upper, oxidised zone, that is rich
in Limonite, formed by the oxidation of Pyrite, and often carrying attractive,
crystallised minerals.
Etymology and history
The name Pyrite is derived from Greek 'pyr' meaning fire, alluding to the fact that
Pyrite forms sparks when rubbed against steel, the name has, however, been used
indiscriminately during history. 'Pyrites' (note plural) commonly shows up particularly
in older English-language literature describing a range of yellow or golden sulfides,
including Chalcopyrite, Pyrrhotite, Marcasite, and others. Often 'iron Pyrites' will mean
Pyrite in the modern sense, but that too may include at least Pyrrhotite and Marcasite,
but not Chalcopyrite. Sometimes Chalcopyrite has been called 'copper Pyrite' for rather
obvious reasons. This obfuscation goes back to Antiquity, where a.o. Dioscorides (app.
50) describes Pyrite as a copper ore, but acknowledges it sometimes carries no copper -
Chalcopyrite is rich in copper, Pyrite contains none. This pervades the works of
subsequent authors, from Pliny's (77) Natural History through the Renaissance scholar
Agricola's (1556) De Re Metallica. The latter corresponds to the German use of the
word 'Kies', more recently modified with qualifiers like 'Kupferkies' (Chalcopyrite),
Schwefelkies (Pyrite), Speerkies (Marcasite), and Magnetkies (Pyrrhotite).
Pyrite is often called 'fools gold' because of its metallic, golden colour, but is easily
distinguished from gold - gold is denser and softer than Pyrite, gold is malleable, Pyrite
is brittle, and chemically they are completely different. But do note, that Pyrite is often
an associate of Gold in Gold specimens. Chemically, Pyrite is an iron disulfide, but it
may carry impurities of nickel or cobalt, replacing some of the iron.
Pyrite forms attractive crystals, most frequently is simple cubes or
pentagondodecahedra, occasionally octahedra or other forms. Pyrite from a few deposits
form unusual twins of pentagondodecahedra, called 'iron cross twins' because the
protruding edges of the two pentagondodecahedra resemble the German 'iron cross'
medal, styled on a Maltese cross. Pyrite is unstable under normal open-air conditions,
and easily decomposes. This may produce exotic sulfate minerals (e.g., Melanterite) or
spectacular pseudomorphs of Limonite after Pyrite, perfect 'Pyrite crystals' replicated in
chocolate brown Limonite.
Incomplete Pyrite
In our view, some of the most spectacular Pyrite specimens are the incomplete ones -
that is, some of the incomplete ones. The Witwatersrand Complex carries a magnificent
conglomerate of 'beach pebbles', some of which are composed of Pyrite - that is, grains
of Pyrite that has been rounded as beach pebbles. The conglomerate is cemented from
pebbles, and was formed in the Precambrian, before Earth had appreciable oxygen in
the atmosphere - that is why the Pyrite pebbles survived. Sure, Pyrite crops out in beach
environments all over the World today, but you never find it as beach pebbles because it
oxidises too fast. The deposit at Hnusta in the Czech Republic represents a variation of
that theme. There you can find quite large pentagondodecahedral Pyrite crystals that
appear 'rounded' or 'worn', but are imbedded in a schist. They are indeed worn, but
they are worn by another process than the pebbles of Witwatersrand. Movements in the
rock caused the Pyrite crystals to 'roll' and get abraded - that is, they too got abraded in
an oxygen-free environment, albeit by another process.
Specimen of
Pyrite crystals from Tasna in Bolivia
Pyrite use
Pyrite is an iron disulfide, but is not used primarily for iron ore even if it locally occurs
in very large deposits. It is very costly and environmentally undesirable to burn off the
sulfur from Pyrite, and it is difficult to purify the ore for high-grade steels, that can not
contain any sulfur. It is far more beneficial to process the traditional oxide iron ores,
Hematite and Magnetite. Pyrite is, however, quarried extensively to produce sulfuric
acid. The Pyrite is roasted with excess oxygen to produce sulfur trioxide, that forms
sulfuric acid when combined with water. The roast residue, iron oxide, may then be
processed as iron ore, but by volume this is insignificant compared to other iron ores.
You may wonder why Pyrite is used for this purpose, rather than native Sulfur. There
are number of reasons, including that Pyrite has a high weight-percent sulfur (app.
53%) and it is simple to get rather pure Pyrite, but only few Sulfur deposits supply ore
with over 53% Sulfur. Furthermore, the residue from processing Pyrite can be used, the
residue from processing native Sulfur (often volcanic ash) is worthless, and needs to be
deposited.
Pyrite in collections
.
Pyrite can be a bit tricky to store in collections. Particularly very fine-grained Pyrite, as
that replacing fossils, is prone to decompose if exposed to humidity, whereas large
crystals as known from for example Elba (Italy), Logrono (Spain) or Huanzala (Peru)
are far more stable. Note, though, it is an inherent property of the mineral, and even
large crystals should be stored dry and preferably at low temperatures. The problem
about the decomposition is not just that you loose a specimen, but that during the
decomposition it forms sulfuric acid, that will destroy labels, boxes, the bottom of your
drawer, etc. Whatever is made from paper, cardboard, wood, or most metals is attacked
by the acid.
Pyrite associates
Pyrite being common and wide-spread means, it may occur with any of a number of
minerals. My records indicate that Pyrite from a range of deposits occurs on specimens
that also carry one or more of the following minerals: Achantite, Actinolite, Aikinite,
Albite, Altaite, Anatase, Ancylite, Andradite, Anglesite, Anhydrite, Ankerite,
Annabergite, Apatite, Apophyllite, Apuanite, Aragonite, Arsenopyrite, Augelite,
Autunite, Azurite, Barbosalite, Barite, Baumhauerite, Bementite, Benjaminite,
Berthierine, Bertrandite, Betpakdalite, Biotite, Bismuth, Bismuthinite, Bornite,
Boulangerite, Bournonite, Brannerite, Brookite, Bustamite, Calaverite, Calcite,
Carbonat-hydroxylapatite, Cassiterite, Cerussite, Chabazite, Chalcocite, Chalcopyrite,
Chamosite, Chernovite, Chiolite, Chrysocolla, Cinnabarite, Coloradoite, Columbite,
Colusite, Cookeite, Cordierite, Corundum, Covellite, Cronstedtite, Cryolite,
Cryolithionite, Dachiardite var. Na-Dachiardite, Dannemorite, Datolite, Davidite-(La),
Dawsonite, Derbylite, Digenite, Diopside, Dolomite, Dufrenoysite, Emplectite, Enargite,
Epidote, Euxenite, Ferberite, Fergusonite, Ferrinatrite, Ferrohornblende, Fizelyite,
Fluoborite, Fluorite, Franckeite, Freibergite, Friedrichite, Gadolinite, Galena,
Gearksutite, Gersdorffite, Glauconite, Glaucophane, Goethite, Gold, Gorceixite,
Graphite, Gratonite, Greigite, Gypsum, Hagendorfite, Hedenbergite, Hematite,
Hemimorphite, Hessite, Heyrovskyite, Hübnerite, Hureaulite, Hutchinsonite,
Hypercinnabar, Ikunolite, Ilesite, Illite, Imhofite, Jamesonite, Jarlite, Johannsenite,
Jordanite, Junoite, Keckite, Kermesite, Kidwellite, Kingsmountite, Kotoite, Kutnohorite,
Kyanite, Laitakarite, Laueite, Lazurite, Lengenbachite, Leucophosphite, Linarite,
Linneite, Liveingite, Ludlamite, Luzonite, Magnesite, Magnetite, Malachite, Marcasite,
Maricite, Melanterite, Melonite, Messelite, Metacinnabar, Miargyrite, Microcline,
Millerite, Mineral Lu, Mitridatite, Molybdenite, Morenosite, Muscovite, Naumannite,
Neotocite, Nepheline, Norsethite, Oligoclase, Orpiment, Orthoclase, Osarizawaite,
Owyheeite, Pachnolite, Palygorskite, Pararealgar, Pavonite, Petzite, Phlogopite,
Phosphoferrite, Phosphosiderite, Platinum, Polybasite, Polymignite, Prehnite, Prosopite,
Pyrargyrite, Pyrochlore, Pyrolusite, Pyromorphite, Pyrophyllite, Pyrostilpnite,
Pyrrhotite, Quartz, Quintinite-2H, Ralstonite, Rathite, Rauenthalite, Realgar, Reddingite,
Rhodochrosite, Rhodonite, Richterite, Robertsite, Rockbridgeite, Rozenite, Rutile,
Samsonite, Sarcopside, Sartorite, Satterlyite, Schafarzikite, Scheelite, Schoonerite,
Schšrl, Schulenbergite, Scolecite, Scorzalite, Siderite, Siegenite, Silver, Smithsonite var.
Co-Smithsonite, Smythite, Sphalerite, Stannite, Stellerite, Stenonite, Stephanite,
Stewartite, Stibnite, Stilbite, Strengite var. Cu-Strengite, Strontiodresserite, Strunzite,
Sylvanite, Szaibelyite, Teallite, Tellurobismuthite, Tennantite, Tetradymite,
Tetrahedrite, Thaumasite, Thomsenolite, Thuringite, Titanite, Topaz, Tremolite var.
Byssolite, Triphylite, Tsumoite, Uraninite, Valleriite, Versiliaite, Vivianite, Wagnerite,
Wavellite, Weberite, Weibullite, Whewellite, Wittite, Wolfeite, Wolframite,
Woodhouseite, Wulfenite, Zinkenite, Zinnwaldite, Zircon, and Zwieselite.
Specimen Handling
As mentioned above, Pyrite may decompose, if stored in humid conditions. The simplest
prevention seems to be to store Pyrite specimens dry (less than 40% relative humidity),
ideally in a sealed bag or glass jar with desiccator silica gel (get the one changing colour
when it absorbs water so you know when to replace it). Note that ordinary plastic bags
are not humidity proof, and the silica gel should not touch the specimen. And no, you
can not varnish your Pyrite specimen - sure, you can, but it will not protect the
specimen at all. All varnishes are porous, and humidity easily passes through. Ask your
local natural history museum where to buy supplies, if you wish to go this way. Some of
the references in the bibliography offer suggestions on how to preserve Pyrite, but note
they are not necessarily up to the current understanding and may dispense erroneous
advise. Pyrite specimens can be fragile and should be handled with care like any other
mineral specimen.
Bibliography
Agricola, Georgius. 1556 (and subsequent editions, several languages). De Re
Metallica [translated by Herbert Clark Hoover & Lou Henry Hoover, 1912, 1950,
1986]
Anthony, John Williams, Richard A. Bideaux, Kenneth W. Bladh & Monte C.
Nichols. 1990. Handbook of mineralogy, vol. 1
Bancroft, Peter. 1984. Gem & Crystal Treasures.
Bayliss, Peter. 1977. Crystal structure refinement of weakly anisotropic Pyrite.
American Mineralogist, 62(11-12), 1168-1172
Bayliss, Peter. 1989. Crystal chemistry and crystallography of some minerals
within the Pyrite group. American Mineralogist, 74(9-10), 1168-1172
Blackburn, William H. & William H. Dennen. 1997. Encyclopedia of mineral
names. Canadian Mineralogist, special publication 1.
Croucher, R. & Alan R. Woolley. 1982. Fossils, minerals and rocks, collection
and preservation.
Gaines, Richard W., H. Catherine W. Skinner, Eugene E. Foord, Brian Mason,
Abraham Rosenzweig & Vandall T. King. 1997. Dana's new mineralogy: the
system of mineralogy of James Dwight Dana and Edward Salisbury Dana, 8th
ed.
Henckel, J. Fr. 1725. Pyritologia oder Kiess-Historie.
Hintze, Carl (ed.) 1898-1904. Handbuch der Mineralogie, vol. 1, section 1.
Kostov, Ivan & Jordanka Minceva Stefanova. 1982. Sulphide minerals. Crystal
chemistry, parageneses and systematics
Noe-Nygaard, Arne. 1966. Mineralogi, 3rd ed.
Palache, Charles, Harry Berman & Clifford Frondel. 1944. The system of
mineralogy of James Dwight Dana and Edward Salisbury Dana, Yale University
1837-1892, 7th ed. vol. 1
Palache, Charles, Harry Berman & Clifford Frondel. 1944. The system of
mineralogy of James Dwight Dana and Edward Salisbury Dana, Yale University
1837-1892, 7th ed. Vol. 1.
Pearl, Richard M. 1947. Mineral collectors handbook.
Pearl, Richard M. 1980 (1982 reprint). Cleaning and preserving minerals, 5th
ed.
Ramdohr, Paul & Hugo Strunz. 1980. Klockmann's Lehrbuch der Mineralogie,
16th ed.
Ramdohr, Paul. 1980. The ore minerals and their intergrowths, 2nd ed., vols. 1-
2
Roberts, Willard Lincoln, Thomas J. Campbell & George Robert Rapp jr. 1990.
Encyclopedia of Minerals 2nd ed.
Sinkankas, John. 1964. Mineralogy.
This page is written and maintaned by Claus Hedegaard
