Goethite
The rust-brown iron oxyhydroxide that forms as meteorites weather on Earth.
Key facts
- Formula
- FeO(OH)
- Family
- Oxides
- Crystal system
- Orthorhombic
What it is
Goethite is an iron oxyhydroxide, a major part of ordinary rust. It forms when iron metal or iron-bearing minerals react with water and oxygen. It is named after the German poet Johann Wolfgang von Goethe, who was also a keen mineral collector.
Where it is found
It is the most common weathering product in meteorites found on Earth, filling cracks and replacing metal and troilite in chondrites and iron meteorites. Its abundance is used to set the weathering grade of finds, from W0, fresh, to W6, heavily altered.
How it is recognised
It is yellow-brown to dark brown, with a yellow-brown streak, in rusty veins and rims. In polished section it is grey with brownish internal reflections.
Did you know?
Hot desert meteorites can turn to goethite and other rust minerals over tens of thousands of years.
Goethite also occurs on Mars, detected by the Spirit rover.