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Gray brown, bronze brown (tarnished), yellow brown, light greyish brown, bronze
3½ - 4½
Specific Gravity:
4.67 - 4.79
Crystal System:
Named after Domenico Troili (1722–1792) who first noted the mineral in a meteorite that fell in 1766 at Albareto, Modena (Italy).

Troilite is the only Italian mineral whose type locality is actually a meteorite impact site. The Abbé Domenico Troili, of the Society of Jesus, is widely credited by those who study meteorites as having written the first description of the fall of a meteorite (“Ragionamento della caduta di un sasso”, published in Modena in 1766). Troili collected reports from many eyewitnesses, closely examined the stone and detected in it small grains of a brassy mineral he called “marchesita”, which was long assumed to be pyrite, FeS2. Only one century later the mineral was recognized to be stoichiometric iron sulphide, FeS.
Pyrrhotite Group. Chemically the S-analogue of achávalite. Also chemically the Fe analogue of covellite, which has the same space group.

Troilite, a native iron protosulphide, and related to the species pyrrhotite (monoclinic or hexagonal Fe1-xS; x = 0 - 0.17; several polytypes known), and smythite (trigonal (Fe,Ni)3+xS4; x = 0-0.3).
Troilite is stoichiometric FeS, without vacancies in its atomic structure, and because of this it is non-magnetic; in contrast, magnetic pyrrhotite is iron-deficient.
Troilite is considered a grandfathered species by IMA CNMNC, though in some respect it could be considered a polytype of pyrrhotite. In fact troilite might transform into hexagonal pyrrhotite at T <122°C (pyrrhotite-2H polytype).

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Classification of TroiliteHide

Approved, 'Grandfathered' (first described prior to 1959)

2 : SULFIDES and SULFOSALTS (sulfides, selenides, tellurides; arsenides, antimonides, bismuthides; sulfarsenites, sulfantimonites, sulfbismuthites, etc.)
C : Metal Sulfides, M: S = 1: 1 (and similar)
C : With Ni, Fe, Co, PGE, etc.

8 : AmXp, with m:p = 1:1

Physical Properties of TroiliteHide

Gray brown, bronze brown (tarnished), yellow brown, light greyish brown, bronze
tarnishes rapidly on exposure
Brownish black
3½ - 4½ on Mohs scale
VHN100=250 - Vickers
None Observed
4.67 - 4.79 g/cm3 (Measured)    4.85 g/cm3 (Calculated)

Optical Data of TroiliteHide


Chemical Properties of TroiliteHide


Crystallography of TroiliteHide

Crystal System:
Class (H-M):
6/mmm (6/m 2/m 2/m) - Dihexagonal Dipyramidal
Space Group:
Cell Parameters:
a = 5.958 Å, c = 11.74 Å
a:c = 1 : 1.97
Unit Cell V:
361.7 ų
massive, granular

X-Ray Powder DiffractionHide

Powder Diffraction Data:
2.98 (40)
2.66 (60)
2.09 (100)
1.923 (30)
1.719 (50)
1.331 (40)
1.119 (40)
Troilite can be recognized in powder photographs by the presence of a 5.18 A line, and the absence of lines with larger spacings (Carpenter & Desborough, 1964).

Type Occurrence of TroiliteHide

Synonyms of TroiliteHide

Other Language Names for TroiliteHide

Simplified Chinese:陨硫铁
Traditional Chinese:隕硫鐵

Relationship of Troilite to other SpeciesHide

Other Members of this group:
Smythite(Fe,Ni)3+xS4 (x=0-0.3)Trig. 3m (3 2/m) : R3m

Common AssociatesHide

Associated Minerals Based on Photo Data:
Kamacite33 photos of Troilite associated with Kamacite on
Iron19 photos of Troilite associated with Iron on
Taenite18 photos of Troilite associated with Taenite on
Olivine9 photos of Troilite associated with Olivine on
Schreibersite8 photos of Troilite associated with Schreibersite on
Rutile6 photos of Troilite associated with Rutile on
Brezinaite6 photos of Troilite associated with Brezinaite on
Meteoritic Iron6 photos of Troilite associated with Meteoritic Iron on
Chromite5 photos of Troilite associated with Chromite on
Albite-Anorthite Series4 photos of Troilite associated with Albite-Anorthite Series on

Related Minerals - Nickel-Strunz GroupingHide

2.CC.05Achávalite(Fe,Cu)SeHex. 6/mmm (6/m 2/m 2/m) : P63/mmc
2.CC.05BreithauptiteNiSbHex. 6/mmm (6/m 2/m 2/m) : P63/mmc
2.CC.05FrebolditeCoSeHex. 6/mmm (6/m 2/m 2/m) : P63/mmc
2.CC.05Langisite(Co,Ni)AsHex. 6 : P63
2.CC.05NickelineNiAsHex. 6/mmm (6/m 2/m 2/m) : P63/mcm
2.CC.05Sederholmitebeta-NiSeHex. 6/mmm (6/m 2/m 2/m) : P63/mmc
2.CC.10Smythite(Fe,Ni)3+xS4 (x=0-0.3)Trig. 3m (3 2/m) : R3m
2.CC.15CherepanoviteRhAsOrth. mmm (2/m 2/m 2/m) : Pnma
2.CC.20MilleriteNiSTrig. 3m : R3m
2.CC.25Mackinawite(Fe,Ni)9S8Tet. 4/mmm (4/m 2/m 2/m) : P4/nmm
2.CC.30VavříniteNi2SbTe2Hex. 6/mmm (6/m 2/m 2/m) : P63/mmc
2.CC.35bCooperitePtSTet. 4/mmm (4/m 2/m 2/m) : P42/mmc

Other InformationHide

Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

Troilite in petrologyHide

References for TroiliteHide

Reference List:
Sort by Year (asc) | by Year (desc) | by Author (A-Z) | by Author (Z-A)
Öfvers. KVA handl. (1868), 25, 197-201.
Haidinger, W. (1863): Meteorit von Albareto im k. k. Hof-Mineralienkabinet vom Jahre 1766, un der troilit: K. Academie der Willenschaften, Vienna (Wien), Mathematisch-naturwissenschaftiche Klasse, Sitzumsberichte, 47, 283-298.
Hägg, G. & Sucksdorff, I. (1933): Die Kristallstruktur von Troilit und Magnetkies. Zeitschrift für Physikalische Chemie, B22, 444-452.
Carpenter, R. H. & Desborough, G. A. (1964): Range in solid solution and structure of naturally occurring troilite and pyrrhotite. Am. Mineral. 49, l350-1365.
Carpenter, H.R. & A.C. Bailey (1973): Application of Ro and Ar measurements to the study of pyrrhotite and troilite: Am. Min.: 58: 440-443.
King, H.E. & Prewitt, C.T. (1982): High-pressure and high-temperature polymorphism of iron sulfide (FeS). Acta Crystallographica, B38, 1877-1887.
Zapiski Vserossiyskogo Mineralogicheskogo Obshchestva (1986): 115: 173-177.
Töpel-Schadt, J. & Müller, W.F. (1992): Transmission electron microscopy
on meteoritic troilite. Physics and Chemistry of Minerals, 8, 175-179.
Scott, E.R.D. and Pinault, L.J. (1999) Partial Melting and Incipient Segregation of Troilite and Metal in Winonaites, Acapulcoites, IAB and IIE Irons, and Fine-Grained H6 Chondrites. XXX Lunar and Planetary Science Conference, Houston, abstract 1507.
Marvin, U.B. & Cosmo, M.L. (2002): Domenico Troili (1766): The true cause of the fall of a stone in Albereto is a subterranean explosion that hurled the stone skyward. Meteoritics & Planetary Science, 37, 1857-1864.
Thomas, J.E., Skinner, W.M., Smart, R.St.C. (2003): A comparison of the dissolution behavior of troilite with other iron (II) sulfides: implications of structure. Geochimica et Cosmochimica Acta, 67, 831-843.
Selivanov, E.N., Vershinin, A.D., and Gulyaeva, R.I. (2003) Thermal expansion of troilite and pyrrhotine in helium and air. Inorganic Materials: 39: 1097-1102.
Ono, S. & Kikegawa, T. (2006): High-pressure study of FeS, between 20 and 120 GPa, using synchrotron X-ray powder diffraction. American Mineralogist, 91, 1941-1944.
Skála, R., Císařová, I., and Drábek, M. (2006) Inversion twinning in troilite. American Mineralogist: 91: 917-921.
Avril C, Malavergne V, Caracas R, Zanda B, Reynard B, Charon E, Bobocioiu E, Brunet F, Borensztajn S, Pont S, Tarrida M, Guyot F (2013) Raman spectroscopic properties and Raman identification of CaS-MgS-MnS-FeS-Cr2FeS4 sulfides in meteorites and reduced sulfur-rich systems. Meteoritics and Planetary Science 48, 1415-1426

Internet Links for TroiliteHide

Localities for TroiliteHide

This map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.

Locality ListShow

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