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Troilite

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Formula:
FeS
System:HexagonalColour:Gray brown, bronze brown ...
Hardness:3½ - 4
Name:Named after Domenico Troili 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.

Troilite, a native iron protosulphide, and related to the species pyrrhotite (monoclinic or hexagonal Fe(1-x)S; x = 0 - 0.17; several polytypes known), and smythite (trigonal (Fe,Ni)(3+x)S4; 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).


Classification of Troilite

IMA status:Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
Explanation of status:It appears to be a polytype of pyrrhotite under the current IMA definition. It is considered a grandfathered species by IMA CNMNC, but, in fact, troilite might be pyrrhotite-2H at T < 122°C.
Strunz 8th edition ID:2/C.19-10
Nickel-Strunz 10th (pending) edition ID:2.CC.10

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.
Dana 8th edition ID:2.8.9.1

2 : SULFIDES
8 : AmXp, with m:p = 1:1
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Type Occurrence of Troilite

Type Locality:Albareto meteorite, Albareto, Modena Province, Emilia-Romagna, Italy
Year of Discovery:1863

Occurrences of Troilite

Geological Setting:Troilite occurs in serpentine, in layered ultramafic intrusives, and in meteorites. Known terrestial occurrences of troilite are not common. Found in a great number of meteorites (also Lunar and Martian) and in planetary nebulae. Found in slags and also in pulverized coal particles after combustion. Based on observations by the Voyager spacecraft in 1979 and Galileo in 1996, troilite seems to be an important phase in the mineral composition of the model rock of Jupiter's Galilean satellites Ganymede and Callisto. Based on the observations of Viking-1 and Viking-2-XRF-soil analyses and Phobos-2 orbital γ-ray data, troilite is likely to be a common mineral in the Martian surface rocks.

Physical Properties of Troilite

Lustre:Metallic
Diaphaneity (Transparency):Opaque
Colour:Gray brown, bronze brown (tarnished), yellow brown, light greyish brown, bronze
Streak:Brownish black
Hardness (Mohs):3½ - 4
Cleavage:None Observed

Crystallography of Troilite

Crystal System:Hexagonal
Class (H-M):6/mmm (6/m 2/m 2/m) - Dihexagonal Dipyramidal
Space Group:P63/mmc
Cell Parameters:a = 5.958Å, c = 11.74Å
Ratio:a:c = 1 : 1.97
Unit Cell Volume:V 361.7 ų
Z:12

Chemical Properties of Troilite

Formula:
FeS
Essential elements:Fe, S
All elements listed in formula:Fe, S

Relationship of Troilite to other Species

Structurally related to group(s):
Pyrrhotite Group
Related Minerals - Nickel-Strunz Grouping):

- +
2.CC.UM2007-26-S:CuFeIrNiPtRh
(Ir,Cu,Ni,Pt,Rh,Fe)
 
9
S
 
11
2.CC.05Achavalite
(Fe,Cu)Se
2.CC.05Breithauptite
NiSb
2.CC.05Freboldite
CoSe
2.CC.05Kotulskite
Pd(Te,Bi)
2.CC.05Langisite
(Co,Ni)As
2.CC.05Nickeline
NiAs
2.CC.05Sederholmite
beta-NiSe
2.CC.05Sobolevskite
Pd(Bi,Te)
2.CC.05Stumpflite
Pt(Sb,Bi)
2.CC.05Sudburyite
(Pd,Ni)Sb
2.CC.05Jaipurite
CoS
2.CC.05Zlatogorite
NiCuSb
 
2
2.CC.10Pyrrhotite
Fe
 
1-x
S (x = 0 to 0.17)
2.CC.10Smythite
(Fe,Ni)
 
3+x
S
 
4
(x=0-0.3)
2.CC.15Cherepanovite
RhAs
2.CC.15Modderite
(Co,Fe)As
2.CC.15Ruthenarsenite
(Ru,Ni)As
2.CC.15Westerveldite
(Fe,Ni,Co)As
2.CC.20Millerite
NiS
2.CC.20Mäkinenite
γ-NiSe
2.CC.20UM1990-38-S:CuFeIrNiPtRh
(Ir,Pt,Ni,Fe)S
2.CC.25Mackinawite
(Fe,Ni)
 
9
S
 
8
2.CC.30Hexatestibiopanickelite
(Pd,Ni)(Sb,Te)
2.CC.30Vavřínite
Ni
 
2
SbTe
 
2
2.CC.35aBraggite
(Pt,Pd,Ni)S
2.CC.35bCooperite
PtS
2.CC.35aVysotskite
(Pd,Ni)S

Other Names for Troilite

Synonyms:
Meteorkies
Other Languages:
German:Troilit
Russian:Троилит
Simplified Chinese:陨硫铁
Spanish:Troilita
Traditional Chinese:隕硫鐵

Other Information

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

References for Troilite

Reference List:

- +
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, 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.

Internet Links for Troilite

Search Engines:
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  • Raman and XRD data at RRUFF project
  • American Mineralogist Crystal Structure Database
  • Troilite details from Handbook of Mineralogy (PDF)
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  • Localities for Troilite

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