Native Iron

As has already been mentioned, iron seldom occurs in the free state in nature on account of the readiness with which it oxidises on exposure to a moist atmosphere. Native iron is frequently of meteoric origin, and contains varying quantities of alloyed nickel. Usually the nickel ranges from 1 to 10 per cent., but the metallic particles contained in the meteorite which fell near Middlesbrough in 1881 possessed no less than 21.32 per cent, of nickel, whilst the Santa Catharina siderite contained 34 per cent., and Oktibbeha County siderite 60 per cent, of nickel. Owing largely to the presence of this element, meteoric iron presents a whitish fracture, and resists corrosion extraordinarily well.

It will be observed that all of the meteorites contain, in addition to nickel, a small quantity of cobalt, whilst the carbon content is extremely small. Carbon is sometimes present in meteoric iron in the form of minute diamonds. The Rowton specimen is interesting as being the first siderite observed to fall in Great Britain, and may be seen in the Natural History Museum, South Kensington. The Perryville siderite is the first recorded instance of the presence of ruthenium in meteoric iron. In addition to traces of this element, traces of iridium, palladium, and platinum were detected.

The largest known meteoric mass is the Ahnighito, brought by Peary from Western Greenland in 1895. It now lies in the New York Museum, and weighs 36| tons.

In 1870 Nordenskidld found some large masses of iron containing 1 or 2 per cent, of nickel at Ovifak in Western Greenland. They weighed 9000, 20,000, and 50,000 lbs. respectively, and, though formerly regarded as meteoric, are now believed to be of terrestrial origin, having been reduced from basalt by some natural process.

Grains of Awaruite, an alloy of nickel and iron, have been found in the sands of certain New Zealand and Canadian rivers, containing as much as 67.6 per cent, nickel. Souesite and Josephinite are names given to similar alloys, the former from British Columbia, and the latter found enclosed within water-worn pebbles in Josephine and Jackson Counties, Oregon, U.S.A. An alloy containing some 7 per cent, of nickel is frequently termed kamasite; one corresponding to the formula Fe₅Ni₃ (38 per cent. Ni), taenite; and FeNi (60 per cent, nickel), octibbehite.

Native iron has been found in the coal measures of Missouri, at depths ranging from 35 to 51 feet, which preclude the possibility of meteoric origin. Most probably the metal has been formed by reduction. The fragments of iron weighed on the average 0.5 gram, but a larger mass of 45.4 grams was also discovered. The metal was soft (hardness on Mohs' scale 4), malleable, and, on fracture, silver-white in appearance. Different specimens yielded the following analyses: -

	I.	II.	III.
Fe	99.16 %	99.39 %	97.10 %
SiO2	0.37 %	0.31 %	1.65 %
C	0.065 %	?	?
P	0.207 %	0.13 %	0.176 %

In no case was cobalt, nickel, or copper present. The densities ranged from 7.43 to 7.88.

The dust showers which at various times have fallen in Italy and Sicily frequently contain grains of metallic iron. Similar grains are found in the sands of the Sahara desert, and it is not improbable that the dust showers referred to are terrestrial phenomena, the sand being transported from the desert by cyclones. In numerous other places small grains of iron have been found, and a terrestrial origin is ascribed to the metal in all of these cases.

Traces of metallic iron have been found in basaltic rocks, such as those from the Giant's Causeway. They were detected by pulverising the rock, separating the magnetic grains, and subjecting them to the action of an acidulated solution of copper sulphate in the field of a microscope. Small depositions of copper in crystalline bunches indicated the presence of traces of native iron. Grains of native iron mixed up with limonite and organic matter have been found in petrified wood. Iron crystallises in the cubic system, its cleavage being octahedral. Hardness 4.5; density, when pure, 7.86 (mean value).

A specimen of what may be termed " native cast iron " is stated by Inostzanzeff to have been obtained from Russian Island, Vladivostok. Analysis showed it to contain

Iron	93.87 %
Carbon (free)	2.87 %
Carbon (combined)	0.33 %
Silicon	1.55 %

and small quantities of manganese, sulphur, etc. In micrographical structure, as well as in composition, the metal resembled cast iron, and it is supposed to have been formed by the interaction of coal and iron ore in a sedimentary rock induced by the heat from an intruded igneous rock.

A carbide of iron occurs as Cohenite (Fe, Co, Ni)₃C, in meteorites in distorted crystals, probably belonging to the cubic system. It possesses a metallic lustre, is tin-white in colour when pure, becoming bronze-yellow upon exposure to air. Hardness 5.5 to 6; density 6.977.