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Pyrrhotite

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St Gotthard basis tunnel (north section), NEAT Construction site, Amsteg, Reuss Valley, Uri, Switzerland
© Peter Haas

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Formula:
Fe
 
7
S
 
8
, (-4M), also given as Fe
 
1-x
S (x = 0 - 0.2)
System:MonoclinicColour:Bronze brown, bronze ...
Lustre:MetallicHardness:3½ - 4
Name:From Greek πνρρός "pyrrhos", flame-colored.


Pyrrhotite Group.

Pyrrhotite is found with pentlandite in basic igneous rocks, veins and metamorphic rocks. It is also often found with pyrite, marcasite and magnetite. It has varying magnetic powers, depending on the number of Fe vacancies in the crystal structure. A related species with no vacancies (and therefore non-magnetic), is called troilite and has been found in meteorites and rarely terrestrially.

Visually similar to smythite.

There are monoclinic and hexagonal pyrrhotite polytypes reported:
pyrrhotite-5H, Fe9S10, hexagonal;
pyrrhotite-6M, Fe11S12, monoclinic;
pyrrhotite-7H, Fe9S10, monoclinic;
pyrrhotite-11H, Fe10S11, hexagonal.

Classification of Pyrrhotite

IMA status:Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
Strunz 8th edition ID:2/C.19-20
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:2.8.10.1

2 : SULFIDES
8 : AmXp, with m:p = 1:1
Hey's CIM Ref.:3.9.1

3 : Sulphides, Selenides, Tellurides, Arsenides and Bismuthides (except the arsenides, antimonides and bismuthides of Cu, Ag and Au, which are included in Section 1)
9 : Sulphides etc. of Fe
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Physical Properties of Pyrrhotite

Lustre:Metallic
Diaphaneity (Transparency):Opaque
Colour:Bronze brown, bronze red, or dark brown
Comment:Tarnishes quickly
Streak:Dark grayish black
Hardness (Mohs):3½ - 4
Hardness (Vickers):VHN100=373 - 409 kg/mm2
Cleavage:None Observed
Parting:Distinct on {0001}
Fracture:Sub-Conchoidal
Density (measured):4.58 - 4.65 g/cm3
Density (calculated):4.69 g/cm3

Crystallography of Pyrrhotite

Crystal System:Monoclinic
Cell Parameters:a = 11.88Å, b = 6.87Å, c = 22.79Å
β = 90.47°
Ratio:a:b:c = 1.729 : 1 : 3.317
Unit Cell Volume:V 1,859.96 ų (Calculated from Unit Cell)
Morphology:Tabular or platy
Twinning:On {1012}
Comment:There are monoclinic and hexagonal polytypes. Clinopyrrhotite (F2/d) Fe7S8 will give Fe0.87S formula. Hexapyrrhotite (P63/mmc) is Fe1-xS where 0
Crystal Atlas:
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Pyrrhotite no.15 - Goldschmidt (1913-1926)
Pyrrhotite - {101}, {001}
Pyrrhotite - {100}, {001}
Pyrrhotite - Contact twin on {10-12}

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Epitaxial Relationships of Pyrrhotite

Epitaxial Minerals:
Galena
Epitaxi Comments:Usually the pyrrhotite is on the galena, but codepositing intergrowths are known. The "six fold" axis of pyrrhotite is parallel to the three fold axis (octahedral axis) in galena.

Optical Data of Pyrrhotite

Type:Anisotropic
Anisotropism:Strong
Pleochroism:Weak

Chemical Properties of Pyrrhotite

Formula:
Fe
 
7
S
 
8
, (-4M), also given as Fe
 
1-x
S (x = 0 - 0.2)
Essential elements:Fe, S
All elements listed in formula:Fe, S
Common Impurities:Ni,Co,Cu

Relationship of Pyrrhotite to other Species

Member of Group:
Pyrrhotite Group:
Related Minerals - Nickel-Strunz Grouping):

- +
2.CC.05Achavalite
FeSe
2.CC.05Breithauptite
NiSb
2.CC.05Freboldite
CoSe
2.CC.05Kotulskite
Pd(Te,Bi)
 
1-2
2.CC.05Langisite
(Co,Ni)As
2.CC.05Nickeline
NiAs
2.CC.05Sederholmite
NiSe beta-NiSe
2.CC.05Sobolevskite
PdBi
2.CC.05Stumpflite
Pt(Sb,Bi)
2.CC.05Sudburyite
(Pd,Ni)Sb
2.CC.05Jaipurite
CoS
2.CC.05Zlatogorite
NiCuSb
 
2
2.CC.10Smythite
(Fe,Ni)
 
9
S
 
11
2.CC.10Troilite
FeS
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
Ni(Te,Sb)
2.CC.30Vavřínite
Ni
 
2
SbTe
 
2
2.CC.35aBraggite
(Pt,Pd,Ni)S
2.CC.35bCooperite
(Pt,Pd,Ni)S
2.CC.35aVysotskite
(Pd,Ni)S
Related Minerals - Hey's Index Grouping:

- +
3.9.3Pyrite
FeS
 
2
3.9.4Marcasite
FeS
 
2
3.9.5Greigite
Fe
2+
 
Fe
3+
2
S
 
4
3.9.6Mackinawite
(Fe,Ni)
 
9
S
 
8
3.9.7Smythite
(Fe,Ni)
 
9
S
 
11
3.9.8Achavalite
FeSe
3.9.9Ferroselite
FeSe
 
2
3.9.10Frohbergite
FeTe
 
2
3.9.11Löllingite
FeAs
 
2
3.9.12Arsenopyrite
FeAsS - (Fe
 
0.90
Co
 
0.10
)AsS
3.9.13Gudmundite
FeSbS

Other Names for Pyrrhotite

Synonyms:
Dipyrite (of Readwin)LeberkiseMagnetic PyriteMagnetic PyritesMagnetischer-Kies
MagnetopyritePyrrhotinePyrrohotiteVattenkies
Other Languages:
Basque:Pirrotita
Catalan:Pirrotina
Czech:Pyrhotin
Dutch:Pyrrhotiet
Finnish:Magneettikiisu
French:Pyrrhotite
German:Pyrrhotin
Magnetkies
Magnetopyrit
Pyrrhotit
Pyrrohotit
Hebrew:פירוטיט
Italian:Pirrotite
Japanese:磁硫鉄鉱
Lithuanian:Pirotinas
Norwegian (Bokmål):Magnetkis
Polish:Pirotyn
Portuguese:Pirrotite
Russian:Пирротин
Simplified Chinese:磁黃鐵礦
Slovak:Pyrotit
Spanish:Pirrotita
Magnetopirita
Pirita Magnética
Pyrrohotita
Swedish:Magnetkis
Ukrainian:Піротин
Varieties:
Cobaltoan PyrrhotiteNickeloan Pyrrhotite

Polytypes for Pyrrhotite

Polytypes:
Pyrrhotite-5C

Other Information

Other Information:Variably magnetic
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 Pyrrhotite

Reference List:Palache, Charles, Harry Berman & Clifford Frondel (1944), The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana Yale University 1837-1892, Volume I: Elements, Sulfides, Sulfosalts, Oxides. John Wiley and Sons, Inc., New York. 7th edition, revised and enlarged, 834pp.: 231-235.

Yund, R.A. & H.T. Hall (1970), Kinetics and mechanism of pyrite exsolution from pyrrhotite: Journal of Petrology: 11: 381-404.

Fleet, M.E. (1971) The crystal structure of a pyrrhotite (Fe7S8). Acta Crystallographica: B27: 1864-1867.

Carpenter, H.R. & A.C. Bailey (1973), Application of Ro and Ar measurements to the study of pyrrhotite and troilite: American Mineralogy: 58: 440-443.

Economic Geology (1975): 70: 824.

Acta Crystallographica (1982): B: 1877.

Nesbitt, H.W., Schaufuss, A.G., Scaini, M., Bancroft, G.M., and Szargan, R. (2001) XPS measurement of fivefold and six-fold coordinated sulfur in pyrrhotites and evidence for millerite and pyrrhotite surface species. American Mineralogist: 86: 318-326.

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.

Powell, A.V., Vaqueiro, P., Knight, K.S., Chapon, L.C. & Sanchez, R.D. (2004): Structure and magnetism in synthetic pyrrhotite Fe7S8: a powder neutron-diffraction study. Phys. Rev., Serie 3.B - Condensed Matter 70, 014415-1 - 014415-12.

Internet Links for Pyrrhotite

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