Telluric iron

Telluric iron, also called native iron, is iron that originated on Earth, but is found in a metallic form rather than as an ore. Telluric iron is extremely rare, with only one known major deposit in the world, located in Greenland.

Material properties

Telluric iron resembles meteoric iron, in that it contains both a significant amount of nickel and Widmanstatten structures. However, telluric iron typically contains only around 3% nickel, which is too low for meteorites. There are two types of telluric iron. Both type 1 and type 2 contain comparable amounts of nickel and other impurities. The main difference between the two is the carbon content.

Type 1

Type 1 telluric iron contains a significant amount of carbon. Type 1 is a white nickel cast-iron, containing 1.7 to 4% carbon and 0.05 to 4% nickel, which is very hard and brittle and does not respond well to cold working. The structure of type 1 consists mainly of pearlite and cementite or cohenite, with inclusions of troilite and silicate. The individual ferrite grains are typically about a millimeter in size. Although the composition of the grains may vary, even within the same grain, they are mostly composed of fairly pure nickel-ferrite. The ferrite grains are connected with cementite laminations; typically 5 to 25 micrometers thick; forming the pearlite.

Type 1 is found as very large boulders, typically ranging from a few tons to tens of tons. The metal could not be cold worked by the ancient Inuit people, (the local inhabitants of Greenland), and proves extremely difficult to machine even with modern tools. Machining of type 1 is possibly best accomplished with a carborundum wheel and water cooling. However type 1 was possibly used as hammer and anvil stones by the Inuit.

Type 2

Type 2 telluric iron also contains around 0.05 to 4% nickel, but typically less than 0.7% carbon. Type 2 is a malleable nickel-iron which responds well to cold working. The carbon and nickel content have a great effect on the final hardness of the cold-worked piece.

Type 2 is found as small grains mixed within basalt rock. The grains are usually 1 to 5 millimeters in diameter. The grains are usually found individually, separated by the basalt, although they are sometimes sintered together to form larger aggregates. The larger pieces also contain small amounts of cohenite, ilmenite, pearlite and troilite. Type 2 was used by the Inuit to make items such as knives and ulus. The basalt was usually crushed in order to release the pea-sized grains, which were them hammered into discs about the size of coins. These flat discs were usually inserted into bone handles so that they slightly overlapped each other, forming an edge that resembled a combination of a knife and a saw.^[1][2]

History

Aside from a very small deposit of telluric iron in Kassel, Germany, which has now been depleted, the only known deposit exists near the area of Disko Bay, in Greenland. Found in the volcanic plains of basalt rock, the material was used by the local Inuit to make cutting edges for tools like knives and ulus. The Inuit were the only people to make practical use of telluric iron.

In the late 1840s, when large boulders of iron were discovered near the Disko Bay area by European explorers, it was assumed that the metal was of meteoric origin, since both contain significant amounts of nickel and both had Widmanstatten structures.

In the late 1870s, K. J. V. Steenstrup first identified the type 2 iron, showing that it also contained Widmanstatten structures. Since the type two was located within volcanic basalt, Steenstrup was able to show that the iron was of terrestrial, or telluric, origin. Steenstrup’s findings were later confirmed by meteorite expert J. Lawrence Smith in 1879, and then by Lorenzen in 1882. The extremely rare telluric iron has been studied ever since.^[3][4]

References

1. ^ Iron and steel in ancient times By Vagn Fabritius Buchwald - Det Kongelige Danske Videnskabernes Selskab 2005 Page 35-37
2. ^ Meteoritic Iron, Telluric Iron and Wrought Iron in Greenland By Vagn Fabritius Buchwald and Gert Mosdal - Kommissionen for videnskabelige Undersogelser i Gronland 1985 Page 19-23
3. ^ Iron and steel in ancient times By Vagn Fabritius Buchwald - Det Kongelige Danske Videnskabernes Selskab 2005 Page 35-37
4. ^ Meteoritic Iron, Telluric Iron and Wrought Iron in Greenland By Vagn Fabritius Buchwald and Gert Mosdal - Kommissionen for videnskabelige Undersogelser i Gronland 1985 Page 19-23