Telluric iron

Iron, native iron or telluric iron
Sawed slab of basalt with bright, metallic native iron inclusions from Uivfaq, Disko Island (size: 7.8 x 3.5 x 0.6 cm)
General
Category	Native mineral
Formula (repeating unit)	Fe
Strunz classification	1.AE.05
Dana classification	1.1.17.1
Crystal system	Cubic
Crystal class	Hexoctahedral (m3m) H-M symbol: (4/m 3 2/m)
Space group	Im3m
Unit cell	a = 2.8664 Å; Z = 2
Identification
Color	Steel-gray to iron-black, white in polished section
Crystal habit	Massive, as interstitial blebs, rare as crystals
Twinning	On {111} and on {112}
Cleavage	{001}; with parting on {112}
Fracture	Hackly
Tenacity	Malleable
Mohs scale hardness	4
Luster	Metallic
Diaphaneity	Opaque
Specific gravity	7.3–7.87
References

Telluric iron, also called native iron, is iron that originated on Earth, and 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.

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 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 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.