Akaganéite
A chlorine-bearing rust that makes iron meteorites flake and crumble in museum drawers.
Key facts
- Formula
- FeO(OH,Cl)
- Family
- Oxides
- Crystal system
- Monoclinic
What it is
Akaganéite is an iron oxyhydroxide whose structure holds chloride in tunnels. It forms where iron corrodes in the presence of chlorine. It is named after the Akagane mine in Japan.
Where it is found
In iron meteorites and metal-rich stony meteorites found on Earth, chlorine from soil and sea salt collects at the boundary between metal and rust. There it forms akaganéite, which releases acid and keeps the corrosion going. This is the main cause of rust bloom, the slow flaking and cracking of meteorites in collections. It has also been found on Mars.
How it is recognised
It forms orange-brown powdery rust, often with droplets of liquid called weeping. It is confirmed by X-ray diffraction or Raman spectroscopy.
Did you know?
Storing meteorites in dry air with a desiccant slows akaganéite growth greatly.
The old idea that meteorites rust because of the mineral lawrencite is now largely explained by akaganéite and chlorine.