iron silicide (FeSi) is a narrow-bandgap semiconductor that has unusual electrical resistivity at low temperatures and magnetic properties. It occurs naturally as the mineral naquite and is also found in meteorites.
It is a chemical compound that combines silicon and a less electropositive element, usually carbon. Silicides can form a solid-state or a liquid phase. They can be structurally closer to borides than carbides, but they are not covalent or ionic molecules.
On Earth, these compounds are often formed in extremely reducing environments such as blast furnaces or lightning strikes. In extraterrestrial samples, such as meteorites and lunar regolith, they are also commonly formed by impact-induced space weathering.
Ureilite meteorites have been found to contain iron silicide minerals including suessite (Fe,Ni)3Si, hapkeite (Fe2Si) and xifengite (Fe5Si3). These minerals are similar to silicides found in brecciated ureilite regolith breccias, which were likely derived from the interior of the parent asteroid.
There is evidence that fulgurites may also produce iron silicide by a reduction mechanism with cellulose, which is the most abundant carbon in our planet’s soil and plants. However, this is not a common occurrence in fulgurites and may require very high temperature and pressure conditions to be generated during the formation process. Alternatively, the presence of elemental aluminum could serve as a reducing agent for these minerals. This possibility is a more likely explanation for the formation of silicides in fulgurites with anthropogenic sources.