Telluric iron

Telluric iron is a rare form of elemental iron that originated on Earth. Most iron on our planet is found as iron ore, which is a mineral containing iron mixed with other elements. This is because nearly all metallic iron was transformed into iron oxides during the Great Oxidation Event about 2 billion years ago. Telluric iron is unique because it exists in a metallic form rather than as an oxide. Its name comes from the Latin word "Tellus," meaning Earth. This distinguishes it from meteoric iron, which comes from outer space.

This metal forms deep within the Earth's mantle and crust. In Greenland, the primary deposits are found in dikes or extrusions. A dike is a fracture in bedrock that has been filled with lava. These deposits often appear alongside graphite-rich feldspar. Scientists believe this carbon-rich environment might prevent the iron from oxidizing. There are several theories about how this happens. It is possible the metal escaped oxidation during geological shifts. Alternatively, iron ores and coal may have subducted and been naturally smelted by the heat of the lava.

Telluric iron is categorized into two distinct types based on carbon content. Type 1 is a white nickel cast-iron containing between 1.7% and 4% carbon. It also contains between 0.05% and 4% nickel. This type is very hard and brittle, making it difficult to shape. It often appears as massive extrusions or boulders weighing tens of tons. Type 2 iron is different because it contains much less carbon, typically under 0.7%. It is a malleable nickel-iron, meaning it is soft enough to be shaped by hammering. Type 2 is usually found as small grains, measuring 1 to 5 millimeters, embedded in basalt rock.

These two types show very different physical properties. Type 1 iron has a structure made of pearlite and cementite, also called cohenite. Its ferrite grains are usually about one millimeter in size. If you were to saw a Type 1 boulder in half, you would find a thick outer shell. The inside is often a porous, sponge-like material that can pulverize when struck. Type 2 iron is much easier to work with. The local Inuit people used Type 2 iron to create practical tools. They would crush basalt to release the small iron grains and hammer them into thin, coin-sized discs.

The history of discovering telluric iron is a story of scientific correction. In 1870, Adolf Erik Nordenskiöld found large iron boulders near Disko Bay, Greenland. He initially believed the metal was meteoric because it contained nickel and Widmanstätten structures. These structures are specific crystalline patterns found in certain metals. In 1871, Gustav Nauckhoff collected large samples and brought them to Europe. These massive pieces are still on display in museums today. A 25-ton block is in Stockholm, a 6.6-ton block is in Copenhagen, and a 3-ton block is in Helsinki.

It was K. J. V. Steenstrup who eventually proved the iron was terrestrial. In 1879, he discovered Type 2 iron grains inside basalt in an old grave at Ekaluit. He noticed the iron was embedded in volcanic basalt that matched the local bedrock. This proved the metal was born from the Earth, not from space. He also observed that the iron was soft enough for the Inuit to use for knives. His findings were confirmed by experts like J. Lawrence Smith and Joh Lorenzen. This discovery changed how scientists understood the presence of elemental iron on our planet.

Today, we know that telluric iron is extremely rare. While minor deposits have been reported in places like Scotland, Ireland, and Russia, the Greenland deposits are the only major ones. The Inuit were the only people to make practical use of this rare material. They created unique tools by inserting overlapping iron discs into bone handles. This created an edge that functioned like a combination of a knife and a saw. Understanding telluric iron helps scientists learn about the chemical processes happening deep inside the Earth's crust.