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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}

About Crystal Atlas

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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

Related to:
  • 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 ratio Co:Ni = 5:1
    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

    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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  • Raman and XRD data at RRUFF project
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