Troilite
An iron sulfide mineral, FeS, common in meteorites and often seen as bronze-coloured nodules in irons.
Troilite is iron sulfide with the simple formula FeS. On Earth it is rare, because most natural iron sulfides contain slightly less iron (the mineral pyrrhotite), but in the oxygen-poor setting of meteorites it is common. It occurs as small grains in chondrites and achondrites and as rounded or elongated nodules, sometimes several centimetres across, in iron meteorites. It is named after Domenico Troili, an Italian priest who described the meteorite that fell at Albareto in 1766.
Troilite has played a central role in science. Troilite from the Canyon Diablo iron, which made Meteor Crater in Arizona, contains almost no uranium, so its lead preserves the starting composition of Solar System lead. In 1956 Clair Patterson used it to help calculate the age of the Earth at about 4.55 billion years. Canyon Diablo troilite also became the reference standard for sulfur isotope measurements.
In a cut iron meteorite, troilite appears as bronze to brassy patches, often rimmed by bright schreibersite or graphite. It is only weakly magnetic at most, tarnishes over time and is softer than the surrounding metal.
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