PYRITES, a name employed by mineralogists to designate a large group or family of minerals, compounds of metals with sulphur, or with arsenic, or with both. They are crystalline, hard, generally brittle, and generally yellow. The name pyrites originally belonged to the sulphuret of iron, known as IRON PYRITES; and was given to it in con sequence of its striking fire With steel (Gr. Tyr, fire), so that it was used for kindling powder in the pans of muskets before gun-flints were introduced. Iron pyrites is com monly of a bright brass yellow color; it is often found crystallized in cubes in which form small crystals of it are abundantly disseminated in some roofing-slates; and very large ones occur in some of the mines of Cornwall; it is also found crystallized in dodecahe drons and other forms, more rarely in oblique four-sided prisms; and it often occurs mas sive, globular, stalactitic, capillary, or investing other minerals as an incrustation. Beau tiful specimens of globular iron pyrites are found in the chalk of England. It is a very widely diffused and plentiful mineral, and seems to belong almost equally to all geological formations. It is too abundant in many coal-fields, the action of water and air changing it into sulphate of iron (vitriol), during which change so much heat is evolved that the coal is frequently kindled by it, mines become unworkable, and the progress of the fire can only be stopped, if at all, by building up portions of them to cut off the access of air, or by the admission of a plentiful supply of water. At Quarreltown, in Renfrewshire, a deep hollOw may still be seen, where, about a century ago, the ground fell in, in conse quence of a subterranean fire thus kindled. The color of iron pyrites has often caused it to be mistaken for cold, a mistake which its hardness and comparative lightness should prevent, or its ready solubility in nitric acid, and its burning before the blowpipe on charcoal with bluish flame and smell of sulphur. But it sometimes does contain a small
proportion of gold, sometimes even in visible grains. This auriferous iron pyrites is found in Siberia and in South America. Iron pyrites is never used as an ore of iron, but it is much used for the manufacture of sulphuric acid, and sulphur is obtained from it by sublimation. It is also used for the manufacture of alum. A variety of iron pyrites of a very pale color is called marcasite. There is also a magnetic variety. Corrnit PYRITES, also called yellow copper and chalcopyrite, is the most abundant of all the ores of copper, and yields a large proportion (perhaps a third)of the copper used in the world It is brass-yellow, the color varying with the amount of copper which it contains, a rich color indicating much copper, and a pale color the presence of a comparatively large amount of iron; for this ore is not a sulphuret of copper, but of copper and iron. It occurs massive and disseminated in rocks of almost every class; and is often found crystallized in octahedrons and tetrahedrons, but generally in very small crystals. It may at dace be distinguished from iron pyrites by its comparative softness, yielding readily to the knife, and by the green color of its solution in nitric acid. Before the blowpipe, with borax and soda, it yields a head of copper. COBALT PYRITES, or cabal *be, a sulphuret and arseniuret of copper, is a principal ore of cobalt. It is generally of a silver-white color, and occurs massive, disseminated, or crystallized in cubes, octa hedrons, dodecahedrons, and polyhedrons, in primitiVe rocks. NICEEL PYRITES. also called and nicketine, used as an ore of nickel, is a compound of nickel and arsenic. It is generally found massive, and is of a copper-red color.