Cohenite
An iron–nickel carbide found in many iron meteorites, the natural cousin of cementite in steel.
Key facts
- Formula
- (Fe,Ni)3C
- Family
- Phosphides, carbides, nitrides and silicides
- Crystal system
- Orthorhombic
- First described
- the Magura iron meteorite, 1889
Cohenite was described in 1889 from the Magura iron meteorite of Slovakia and named after Emil Cohen, a German mineralogist who studied meteorites. Its iron-only equivalent, cementite, is a familiar ingredient of steel.
What it is
Cohenite is a carbide: iron and nickel combined with carbon. It is hard and brittle. In steel the same compound without nickel, called cementite, gives hardness.
Where it is found
It occurs as elongated crystals in low-nickel IAB irons such as Canyon Diablo and Magura, in some other irons, and in enstatite chondrites and ureilites. Over very long times at moderate temperature it can break down into metal and graphite.
How it is recognised
On etched slices it appears as bright, tin-white crystals with high relief, often with a yellowish tint. It is magnetic.
Did you know?
Cohenite is rare on Earth but has been found in native iron from Disko Island in Greenland.
Its presence shows that the metal in IAB irons was rich in carbon.