This mineral is found in masses of different form and size in most of the iron mines of Europe and America, and, when submitted to the furnace, it yields a considerable proportion of metal. It makes excellent bar iron, but very indifferent cast iron. In Sweden, and particularly at Roslager, magnetic iron stone is found quite pure, and the iron that is wrought from it is imported in considerable quantities into Great Britain, for the purpose of being manufactured into steel.
The appellation of load, or leading stone, has been given to this kind of iron from its magnetic virtues; for it is not only endowed with the property of attracting iron, but also of pointing itself, and even enabling a needle touched with it to point, towards the poles of the world. We are, however, entirely ignorant what is the cause of this very extraordinary property.
Artificial magnets, constructed of steel, not only possess all the essential virtues of the genuine loadstone, but even in a much higher degree. The natural magnet is consequently now little esteemed except as an object of curiosity.
236. PYRITES, or MARCASITE, is a mineral substance, formed by a combination of iron with sulphur.
It is usually of a bronze, yellow, or brownish colour, very various in form, being massive, globular, club-shaped, oval, or crystallized; and so hard as to strike fire with flint.
Few minerals are more common than this, as it occurs, in some state or other, in almost every rock and vein. It is often found among coals; and, when heated, decrepitates with a loud unpleasant noise and sulphureous smell. To the decomposition of this mineral it is that the hot temperature of almost all the mineral waters may be ascribed.
The name of pyrites, which in the Greek language signifies firestone, has been obtained by this mineral from its property of striking sparks from steel. It was formerly used for fire-arms, as we now use flints. In commerce it is known by the name of marcasite. Some years ago it was much used, particularly in France, for the making of buttons and buckles; and was cut and polished, by lapidaries, for trinkets, particularly for the rims and hands of watches, and various kinds of female ornaments. If skilfully cut in the form of small rose diamonds, although an opaque substance, it has somewhat the appearance of a diamond. In the tombs of the Peruvian princes, with whom a considerable portion of their valuables was always interred, there have been found polished plates of marcasite, which appear to have served them as mirrors.
This mineral is never worked as an ore of iron; and it is principally valued on account of the sulphur which can be obtained from it by means of heat; and the green vitriol, or copperas ([208]), which it affords by exposure to the air.
Ignorant persons frequently mistake iron pyrites for gold; but it is easily distinguished from that precious metal by its brittleness. It breaks when hammered, whereas gold is malleable, or may be extended by hammering: it also strikes fire with steel, which gold will not.
237. RED OCHRE, REDDLE, or RED CHALK, is an iron ore of blood-red colour, which is sometimes found in powder, and sometimes in a hardened state. It has an earthy texture, and stains the fingers when handled.