Troilite
The stoichiometric iron sulfide FeS — rare on Earth but a standard component of iron meteorites.
Intro adapted from Wikipedia (CC BY-SA).
Troilite is an IMA-recognized mineral species in the sulfide class, with the chemical formula FeS.
It crystallizes in the hexagonal crystal system (space group P6_3/mmc).
Key properties: Mohs hardness 3.5–4.5; specific gravity 4.67–4.79; Dark grayish brown streak; Metallic. Anisotropism: Strong. R1 –R2: (400) 24.3–28.4, (420) 24.9–29.6, (440) 25.8–30.9, (460) 27.1–32.6 luster.
IMA symbol Tro, grandfathered status — known before the IMA’s founding, named in 1863.
Found in serpentine (Del Norte Co., California, USA); with Fe–Cu–Ni sulfides in a layered ultramafic intrusive (Sally Malay deposit, Australia); and as nodules in meteorites.
It is found associated with Pyrrhotite, pentlandite, mackinawite, cubanite, valleriite, chalcopyrite, pyrite (Wannaway deposit, Australia); daubréelite, chromite, sphalerite, graphite.
In honor of Dominico Troili (1722–1792), Italian Jesuit, who described, in 1766, a meteorite which fell in Albareto, near Modena, Italy, which contained the species.