Troilite

Troilite
Polished and etched surface of the Mundrabilla meteorite from Australia. The darker brownish areas with striations are troilite with exolved daubréelite.
General
Category	Sulfide mineral
Formula (repeating unit)	FeS
IMA symbol	Tro[1]
Strunz classification	2.CC.10
Crystal system	Hexagonal
Crystal class	Ditrigonal dipyramidal (6m2) H-M symbol: (6m2)
Space group	P62c
Unit cell	a = 5.958, c = 11.74 [Å]; Z = 12
Identification
Color	Pale gray brown
Crystal habit	Massive, granular; nodular; platey to tabular
Cleavage	None
Fracture	Irregular
Mohs scale hardness	3.5–4.0
Luster	Metallic
Streak	Gray black
Diaphaneity	Opaque
Specific gravity	4.67–4.79
Alters to	Tarnishes on exposure to air
References	[2][3][4]

Troilite (/ˈtrɔɪlaɪt/) is a rare iron sulfide mineral with the simple formula of FeS. It is the iron-rich endmember of the pyrrhotite group. Pyrrhotite has the formula Fe_(1-x)S (x = 0 to 0.2) which is iron deficient. As troilite lacks the iron deficiency which gives pyrrhotite its characteristic magnetism, troilite is non-magnetic.^[3]

Troilite can be found as a native mineral on Earth but is more abundant in meteorites, in particular, those originating from the Moon and Mars. It is among the minerals found in samples of the meteorite that struck Russia in Chelyabinsk on February 15th, 2013.^[5] Uniform presence of troilite on the Moon and possibly on Mars has been confirmed by the Apollo, Viking and Phobos space probes. The relative intensities of isotopes of sulfur are rather constant in meteorites as compared to the Earth minerals, and therefore troilite from Canyon Diablo meteorite is chosen as the international sulfur isotope ratio standard, the Canyon Diablo Troilite (CDT).