Magnetite
The strongly magnetic iron oxide that grew in water inside carbonaceous asteroids and forms the crust of cosmic spherules.
Key facts
- Formula
- Fe3O4
- Family
- Oxides
- Crystal system
- Cubic
What it is
Magnetite is an iron oxide containing iron in two charge states. It is the most magnetic natural mineral. Grains can record the magnetic field present when they formed.
Where it is found
In CI chondrites and the Ryugu and Bennu samples it forms spherical framboids like tiny raspberries, stacks of plates and needles, all grown in liquid water inside the parent body. It is also common in CV and CK chondrites, in the fusion crust of meteorites and in iron-rich micrometeorites, and as a weathering product of metal.
How it is recognised
It is black, strongly magnetic and has a black streak. In polished section it is grey with a faint brown tint. Its distinctive shapes in carbonaceous chondrites are clear under an electron microscope.
Did you know?
Magnetite stacks in Ryugu grains look like piles of coins.
Magnetite crystals in the Martian meteorite ALH 84001 were once suggested as possible signs of life, a claim that remains unproven.