1. Native iron A. Pure.—This species is very rare, and its existence was long matter of dispute; though it has been undoubtedly found not only in volcanic formations, but in veins properly so called. It is not entirely like our malleable iron; but is whiter, more ductile, more permanent or less oxidizable in the air, and somewhat less dense. Among the best attested examples of pure native iron is that observed by M. Schreber, in the mountain of Oulle near Grenoble. The metal was entangled in a vein running through gneiss, and appeared in ramifying stalactites, enveloped in fibrous brown-oxide of iron mixed with quartz and clay.
B. The native nickeliferous or meteoric iron is very malleable, often cellular, but sometimes compact, and in parallel plates, which pass into rhomboids or octahedrons. It is naturally magnetic, and by its nickel is distinguishable from terrestrial native iron. Macquart, in describing the famous mass found at mount Kemir in Siberia, says that the iron is perfectly flexible, and fit for making small instruments at a moderate heat; but in too strong a fire, the metal becomes short, brittle, and falls into grains under the hammer. Meteoric iron is covered with a sort of varnish which preserves its surface from the rusting action of the air; but this preservative property does not extend to the interior. Chladni has given a list of masses of meteoric iron, which have been known to fall at different times from the atmosphere, and of many specimens which indicate their atmospheric origin, by their aspect and composition. A portion of the mass of meteoric iron found at Santa-Rosa near Santa-Fe-de-Bogota, was made into a sword, and presented to Bolivar.
C. Native steel-iron.—This substance has all the characters of cast-steel; it occurs in a kind of small button ingots, with a finely striated surface, and a fracture exceedingly fine grained. It is hardly to be touched by the file, and will scarcely flatten under the hammer. M. Mossier found this native steel at the village of Bouiche, near Nery, department of the Allier, in a spot where there had existed a seam of burning coal. A mass of 16 pounds and 6 ounces of native steel was discovered in that place, besides a great many small globules.
2. Arsenical iron, Arsenikkies or Mispickel, is a tin-white mineral, which emits a garlic smell at the blowpipe, or even when sparks are struck from it by steel, accompanied with a small train of white smoke. It contains generally more or less sulphur and sometimes a little silver, associated with metallic arsenic and iron.
3. Yellow sulphuret of iron, commonly called Marcasite, or Martial pyrites. The bronze or brass-yellow colour enables us to recognize this mineral. At the blowpipe it gives off its sulphur, and is converted into a globule attractable by the blowpipe. It is a bisulphuret of iron containing 32 of sulphur and 28 of metal.
Copper pyrites may be distinguished from it by its golden yellow colour, which is frequently iridescent, and by its inferior hardness; for it does not strike fire with steel, like the preceding persulphuret. There is no vein, stratum, or mass of metallic ore which does not contain some iron pyrites; and it is often the sole mineral that fills the veins in quartz. It sometimes contains gold, and at other times silver.
4. White sulphuret of iron.—This is distinguishable from the preceding species only by its colour and form of crystallization, and was hence till lately confounded with it by mineralogists. Its surface is often radiated.
5. Magnetic sulphuret of iron, the Magnetkies of the Germans.—This ore is attractable by the magnet like common iron. Its colour is reddish-yellow, passing into brown; its fracture is rough. It consists of 16 of sulphur and 28 of iron.
6. Black oxide of iron, magnet ore, or native loadstone.—One variety of this species has two poles in each specimen, which manifest a repulsive action against the corresponding poles of a magnetic needle. All the varieties furnish a black powder. Its external colour is a gray approaching to that of metallic iron, but somewhat duller; with occasional iridescence of surface. Neither nitric acid nor the blowpipe has any action upon it. Its specific gravity varies from 4·24 to 5·4; and its constituents are 71·86 peroxide, and 28·14 protoxide, according to Berzelius; or in 100 parts, 71·74 of metallic iron, and 28·26 of oxygen. Assuming the prime equivalent of iron to be 28, with the British chemists, then an ore consisting, like the above, of two prime proportions of peroxide, and one of protoxide, would be represented by the number 116 = 80 + 36; and would consist in 100 parts, of iron 72·4, oxygen 27·6.
Magnetic iron-ore belongs to primitive rock formations, and occurs abundantly in Sweden, Dalecarlia, Norway, Siberia, China, Siam, and the Philippine Isles; but it is rare in England and France. It is worked extensively in Sweden, and furnishes an excellent iron.