Mackinawite
A layered iron sulphide that forms at low temperatures, found in some carbonaceous and iron meteorites.
Key facts
- Formula
- (Fe,Ni)1+xS
- Family
- Sulphides
- Crystal system
- Tetragonal
What it is
Mackinawite is an iron sulphide with a layered structure, often with some nickel. It is one of the first iron sulphides to form when dissolved iron meets sulphide in water at low temperature, and it changes in time to more stable sulphides. It is named after a mine in Washington State.
Where it is found
It occurs as fine intergrowths with troilite, pentlandite and tochilinite in CM chondrites and as thin lamellae in troilite of some iron meteorites, where it probably grew during weathering or very slow cooling.
How it is recognised
It is pinkish grey and strongly anisotropic in reflected light, and is confirmed by microprobe and diffraction.
Did you know?
Mackinawite is thought to have been important in the chemistry of early life on Earth, near undersea vents.
In CM chondrites it can be mistaken for tochilinite, a related layered mineral.