Troilite
Iron sulphide, the bronze mineral found in almost every meteorite.
Key facts
- Formula
- FeS
- Family
- Sulphides
- Crystal system
- Hexagonal
- First described
- the Albareto meteorite (named 1863)
Troilite was named in 1863 by the Austrian mineralogist Wilhelm Haidinger after Domenico Troili, an Italian priest who described the fall of the Albareto meteorite in 1766 and the iron sulphide inside it. It is rare on Earth but common in meteorites.
What it is
Troilite is iron sulphide with exactly one iron atom for every sulphur atom. On Earth the similar mineral pyrrhotite, slightly short of iron, is far more common, because troilite needs conditions very poor in oxygen and sulphur.
Where it is found
It makes up about 5% of most ordinary chondrites, as grains next to metal, and forms rounded nodules up to several centimetres across in iron meteorites, often with graphite, schreibersite and chromite. It is also found in achondrites, pallasites, lunar rocks and the Itokawa grains.
Its sulphur isotopes are so uniform that troilite from the Canyon Diablo iron was for decades the international standard for measuring sulphur isotopes.
How it is recognised
It is bronze to brass yellow with a metallic lustre and tarnishes brown. It is not magnetic, unlike the metal beside it. In cut iron meteorites, troilite nodules look like dull bronze blobs.
Did you know?
The international sulphur isotope scale was once called CDT, for Canyon Diablo troilite.
Troilite in iron meteorites can hold traces of the decay products of short-lived radioactive isotopes.