troilite

Troilite is an iron sulfide mineral with the chemical formula FeS. It crystallizes in the hexagonal system and is typically associated with the NiAs-type structure. In hand specimen it presents a metallic luster with a steel-gray to black color and is opaque. It is generally brittle and exhibits little or no cleavage.

Troilite occurs most notably in meteorites, where it is often the dominant sulfide phase and can appear as inclusions within meteoritic metal or as disseminated grains. It is also found in some lunar rocks and, more rarely, in terrestrial ultramafic sulfide deposits. In meteorites, troilite commonly occurs alongside other sulfides such as pyrrhotite and pentlandite, and it provides information about a body’s thermal history and differentiation.

The mineral forms under high-temperature, reducing conditions and remains stable under those environments. It is of particular interest in planetary science because its presence and isotope compositions help researchers study the early solar system, metal-silicate partitioning, and the evolution of planetary bodies. On Earth, troilite can weather to iron oxides or sulfates, so primary extraterrestrial samples are typically preferred for study.

Summary: troilite is the FeS iron sulfide mineral, hexagonal in structure, with a metallic appearance, best known for its prominence in meteorites and relevance to studies of planetary formation and history.