PYRITE or PYRITES, a term applied to iron disulphide when crystallized in the cubic system. The original word pyrites (from Gr. rOp, fire) had reference to the fact that sparks might be elicited on striking the mineral violently, as with flint, so that irvpirns Wog meant a stone which struck fire. Hence the name seems to have been applied also to flint, and perhaps to emery and other hard stones. Nodules of pyrite have been found in pre historic barrows and elsewhere under conditions suggesting their use as a primitive means of producing fire. Even in late historic time it was employed in some of the old wheel-lock guns. The compound is dimorphous, and the modern practice is to dis tinguish the cubic form as pyrite and the orthorhombic as marcasite (q.v.).
Iron pyrites, or pyrite, belongs crystallographically to the parallel-faced hemihedral class of the cubic system. Its common forms are the cube, the octahedron, and the pentagonal dodeca hedron, or various combinations of them. It has 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 colour of pyrite is brass-yellow, whilst that of marcasite when untarnished may be almost tin white. From copper-pyrites (chalcopyrite) pyrite is distin guished by its superior hardness and by its paler colour. On ex posure to meteoric influences pyrite commonly becomes brown, by formation of ferric hydrate. Such a change is very common on the outcrop of mineral veins, forming what miners call "gozzan." According to the formula FeS,, pyrite contains theoretically 46.67% of iron and 53.33% of sulphur. Practically, however, it frequently contains other metals, such as copper, cobalt and nickel. Gold is often present, and in many gold-mining districts the precious metal is obtained mainly from auriferous pyrite. As pyrite, from its brass-yellow colour, is sometimes mistaken for gold, it has been vulgarly called "fool's gold." Traces of thallium, which are present in some pyrite, may be detected in the flues of the furnaces where the metal is roasted. Arsenic is an impurity which may be of serious consequence in some of the purposes to which pyrite is applied. The presence of copper, nickel and ar senic is possibly due in many cases to traces of kindred minerals, like chalcopyrite, pentlandite and mispickel.
Pyrite is a mineral of very wide distribution, occurring under varied conditions and probably originating in various ways. It is common in mineral-veins, usually associated with quartz, and is often known to miners as "mundic." It occurs crystallized, com monly in cubes, in schistose and slaty rocks, and less abundantly in the younger sedimentary deposits. In coal it not infrequently forms bands and nodules known as "brasses," and may also be finely disseminated through the coal as "black pyrites"; but much of the so-called pyrite of coal is really marcasite. Films of py
rite sometimes coat the joint-planes of coal. Pyritous shales have been largely used in the manufacture of alum, and are therefore known as "alum-shales." Many fossils are mineralized with py rite, which has evidently been reduced by the action of decom posing organic matter on a solution of ferrous sulphate, or per haps less directly on ferrous carbonate dissolved in water con taining carbonic acid, in the presence of certain sulphates. A similar action probably explains the origin of pyrite and mar casite in coal and lignite, in clay and shales, and in limestone like chalk.
Pyrite is largely worked for the sake of the sulphur that it con tains, and has displaced sulphur in the manufacture of sulphuric acid. For this purpose its value depends on the proportion of sulphur present. Pyrite low in sulphur is incapable of sustaining its own on without the aid of an external source of heat, and 45% of sulphur is, for economic reasons, usually regarded as the lowest percentage 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 pyrite 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 pyrite, with a notable but variable proportion of copper, sometimes with silver and gold, and not infrequently associated with lead and zinc sulphides. The copper probably exists as disseminated chalcopyrite. Deposits of such cupriferous pyrite are widely distributed and are often of great magnitude. They are generally of lenticular form, and usu ally occur in or near the contact of eruptive rocks with schists or slates; the presence of the igneous rock being probably con nected genetically with their origin.
The world's annual production of iron-pyrite is about 4,500, 000 tons. The largest producer is Spain, with upwards of 2,000, 00o tons, including the cupriferous pyrite. France yields about 200,000 tons, largely from the Sain Bel mines, department of the Rhone. Then follows Portugal, with its important output of cu priferous pyrites. In the United States the production of pyrite now reaches about 170,000 tons per annum. The State of Virginia is the chief producer, followed successively by Georgia, North Carolina, Colorado, Massachusetts, California, Missouri, New York, etc. From Indiana and Ohio a quantity of pyrite is ob tained as a by-product in coal-mining. The United Kingdom yields but little pyrite, the annual output being not more than about 5,000 tons. Large quantities of "sulphur ore" were, how ever, formerly worked in the Vale of Avoca, County Wicklow, Ireland. Finely crystallized specimens of pyrite are obtained from many other localities, especially from Cornwall, Elba and Traversella, near Ivrea, in Piedmont.