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PYRITES

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Originally appearing in Volume V22, Page 693 of the 1911 Encyclopedia Britannica.
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PYRITES , a See also:

term applied to See also:iron disulphide when crystallized in the cubic See also:system, but used also in a See also:general sense to designate a See also:group of metallic sulphides of which this See also:mineral is the most characteristic example. When employed as a group-name the constituent See also:species are distinguished by prefixes: thus the type is called iron pyrites, whilst other species are known as See also:copper pyrites, arsenical pyrites, &c. The See also:original word pyrites (from Gr. aiip, See also:fire) had reference to the fact that See also:sparks might be elicited on striking the mineral violently, as with See also:flint, so that 7rvpir77r AMOos meant a See also:stone which struck fire. Hence the name seems to have been applied also to flint, and perhaps to See also:emery and other hard stones. Nodules of pyrites have been found in prehistoric barrows and elsewhere under conditions suggesting their use as a See also:primitive means of producing fire. Even in See also:late historic See also:time it was employed in some of the old See also:wheel-See also:lock guns. Iron-pyrites was formerly called See also:marcasite, a word variously written marcasin, marchasite, marchesite, marquesite, &c. The two names are now applied to distinct mineral species. The See also:compound FeS2 is dimorphous, and the See also:modern practice is to distinguish the cubic forms as pyrites and the orthorhombic as marcasite (q.v.). Sometimes, however, the term pyrites is loosely applied to both species, and the cubic pyrites is then differentiated by the name " pyrite "—a See also:form which brings the last syllable into See also:harmony with the spelling of the names of most minerals. Iron pyrites, or pyrite, belongs crystallographically to the parallel-faced hemihedral class of the cubic system. Its See also:common forms are the See also:cube, the See also:octahedron, and the pentagonal See also:dodecahedron.

Fig. i shows P the cube (See also:

loo}, d the octahedron (iii and e the pentagonal dodecahedron sr (210}. In fig. 2 7r 12101 and (III} are associated with f the dyakis-dodecahedron 7r {321}; whilst fig. 3 shows a See also:combination of 2r 12101 and it {4211. The faces of the cube are sometimes striated parallel to the edges between P and e (fig. I), the striae on each See also:face being therefore at right angles to those of the adjoining faces, and indicating an oscillatory combination of the cube and pentagonal dodecahedron. Fig. 4 illustrates a characteristic twin, formed by two inter-penetrating pentagonal dodecahedra. Such supplementary twins, known in See also:Germany as " twins of the Iron See also:Cross," are commonly See also:brown by superficial See also:conversion into See also:limonite. Pyrites presents a conchoidal fracture, and a very indistinct cubic cleavage. Its hardness is about 6, and its specific gravity 4•9 to 5.2, being rather more than that of marcasite. Moreover, the See also:colour of pyrites is See also:pale See also:brass-yellow, whilst that of marcasite when untarnished may be almost See also:tin-See also:white.

From copper-pyrites (chalcopyrite) iron-pyrites is distinguished by its See also:

superior hardness and by its paler colour. On exposure to meteoric influences pyrites commonly becomes brown, by formation of ferric See also:hydrate or limonite, whence the See also:change is called " limonitization." Such a change is very common on the outcrop of mineral See also:veins, forming what miners See also:call " gozzan." Another See also:kind of alteration which pyrites may suffer has been termed " vitriolization," since the products are ferrous sulphate, with See also:free sulphuric See also:acid and sometimes a basic ferric sulphate. It is often said that this saline change is more characteristic of marcasite than of pyrite, but according to H. N. See also:Stokes this statement is incorrect. Contrary, too, to popular belief, he has found a fibrous structure more common in pyrite than in marcasite. In some cases the two forms of iron disulphide occur in intimate association and are difficult to distinguish. According to the See also:formula FeS2, pyrites contains theoretically 46'67% of iron and 53.33 of See also:sulphur. Practically, however, it frequently contains other metals, such as copper, See also:cobalt and See also:nickel. See also:Gold is often See also:present, and in many gold-See also:mining districts the See also:precious See also:metal is obtained mainly from auriferous pyrites. As pyrites, from its brass-yellow colour, is sometimes mistaken for gold, it has been vulgarly called " See also:fool's gold." Traces of See also:thallium, which are present in some pyrites, may be detected in the flues of the furnaces where the metal is roasted. See also:Arsenic is an impurity which may be ofserious consequence in some of the purposes to which pyrites is applied.

The presence of copper, nickel and arsenic is possibly due in many cases to traces of kindred minerals, like chalcopyrite, pentlandite and See also:

mispickel. Pyrites is a mineral of very wide See also:distribution, occurring under varied conditions and probably originating in various ways. It is common in, mineral-veins, usually associated with See also:quartz, and is often known to miners as " mundic." It occurs crystallized, commonly in cubes, in schistose and slaty rocks, and less abundantly in the younger sedimentary deposits. In See also:coal it not infrequently forms bands and nodules known as " See also:brasses," and may also be finely disseminated through the coal as " See also:black pyrites "; but much of the so-called pyrites of coal is really marcasite. Films of pyrites sometimes coat the See also:joint-planes of coal. It is believed that the bluish colour of many See also:clays and limestones is referable to the presence of finely divided pyrites, and it is known that certain deposits of See also:blue mud now forming around See also:continental shores owe their colour, in See also:part, to disseminated iron sulphide. Pyritous shales have been largely used in the manufacture of See also:alum, and are therefore known as " alum-shales." Many fossils are mineralized with pyrites, which has evidently been reduced by the See also:action of decomposing organic See also:matter on a See also:solution of ferrous sulphate, or perhaps less directly on ferrous carbonate dissolved in See also:water containing carbonic acid, in the presence of certain sulphates. A similar action probably explains the origin of pyrites and marcasite in coal and See also:lignite, in See also:clay and shales, and in See also:limestone like See also:chalk. Pyrites is largely worked for See also:sake of the sulphur which it contains, and in many cases it has displaced See also:brimstone in the manufacture of sulphuric acid. For this purpose its value depends on the proportion of sulphur present. Pyrites See also:low in sulphur is incapable of sustaining its own See also:combustion without the aid of an See also:external source of See also:heat, and 45% of sulphur is, for economic reasons, usually regarded as the lowest admissible for sulphuric acid manufacture. It is also important for this purpose that the ore should be as free as possible from arsenic (see SULPHURIC ACID).

An extremely important variety of pyrites is that which is more or less cupriferous, and is commonly known commercially as " copper-pyrites ". (q.v.), though distinct mineralogically from that mineral. It consists, indeed, mainly of iron-pyrites, with a notable but variable proportion of copper, sometimes with See also:

silver and gold, and not infrequently associated with See also:lead and See also:zinc sulphides. The copper probably exists as. disseminated chalcopyrite. Deposits of such cupriferous pyrites are widely distributed and are often of See also:great magnitude. They are generally of lenticular form, and usually occur in or near the contact of eruptive rocks with See also:schists or slates; the presence of the igneous See also:rock being probably connected genetically with their origin. Among the best-known deposits of this See also:character are those in the See also:Huelva See also:district, in the See also:south-See also:west of See also:Spain, including the mines of Rio Tinto, Tharsis, Calanas, &c.; with those of See also:San Domingos in See also:Portugal. At Rio Tinto the ore is divided into three classes: (i) The poorest, containing an See also:average of about I i % of copper, which is treated locally by leaching with water and liquor containing ferric sulphate, whereby the copper is dissolved out and afterwards precipitated by See also:pig-iron, whilst the See also:residue is exported as See also:ordinary iron-pyrites. (2) Export ore, with from 2 to 5 % of copper, in which the sulphur, copper and precious metals are utilized, and the residual iron See also:oxide then sold as " See also:purple ore " for use in iron manufacture. (3) Smelting ore, which averages about 6 % of copper, and is treated metallurgically as described under COPPER. The See also:world's See also:annual See also:production of iron-pyrites is about 1,700,000 tons. The largest producer is Spain, with upwards of 350,000 tons, including the cupriferous pyrites.

See also:

France yields about 300,000 tons, largely from the Sain See also:Bel mines, See also:department of the See also:Rhone. Then follows Portugal, with its important output of cupreous pyrites. In the See also:United States the production of pyrites now reaches more than 200,000 tons per annum. The See also:state of See also:Virginia is the See also:chief producer, followed successively by See also:Georgia, See also:North Carolina, See also:Colorado, See also:Massachusetts, See also:California, See also:Missouri, New See also:York, &c. From See also:Indiana and See also:Ohio a quantity of pyrites is obtained as a by-product in coal- PYROLUSITE, a mineral consisting essentially of See also:manganese mining. See also:Newfoundland yields cupreous pyrites, worked at dioxide (MnO2), of importance as an ore of manganese. It is Pilley's See also:Island, whilst the nickeliferous pyrites of See also:Sudbury in a soft, black, amorphous mineral, often with a granular, fibrous See also:Ontario is partly magnetic (see See also:PYRRHOTITE). Magnetic or columnar structure, and sometimes forming reniform crusts. pyrites of commercial importance occurs also in Virginia and It has a metallic lustre, and a black or bluish-black streak, and See also:Tennessee. The United See also:Kingdom yields but little pyrites, readily soils the fingers. The specific gravity is about 4.8. the annual output being not more than about io,000 tons. Supposed crystals of pyrolusite have been proved to be pseudo- Large quantities of " sulphur ore " were, however, formerly morphs after See also:manganite; in fact the mineral often results by the worked in the Vale of See also:Avoca, Co.

See also:

Wicklow, See also:Ireland. Finely dh syr asonnitafrequentlylOOntainsl a littleewater.20TrueO cry tand or alsf of crystallized specimens of pyrite are obtained from many other manganese dioxide are referred to the rare species polianite: they localities, especially from See also:Cornwall, See also:Elba and Traversella, near are tetragonal and isomorphous with cassiterite. Pyrolusite is See also:Ivrea, in See also:Piedmont. I an alteration product of other manganese minerals—manganite, See, for the See also:early See also:history of pyrites, J. F. Henckel's Pyritologia, See also:oder See also:rhodochrosite, See also:rhodonite, &c. It occurs as irregular masses and Kieshistorie (See also:Leipzig, 1725) ; of which an See also:English See also:translation appeared nodules in the residual clayey materials resulting from the decomin 1757, entitled Pyritologia; or a History of the Pyrites, the See also:Principal See also:Body in the Mineral Kingdom. For a modern description of the See also:deposit of pyrites of economic importance reference may be made to A See also:Treatise on Ore Deposits, by J. A. See also:Phillips (2nd ed. by H. See also:Louis, 1896). For chemical means of distinguishing pyrite from marcasite consult H.

N. Stokes, " On Pyrite and Marcasite," See also:

Bull. U. S. Geol. Surv. No. 186 (1901). (F. W.

End of Article: PYRITES

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